Use std::istringstream or std::ostringstream instead of std::stringstream where possible.

This removes std::iostream from the inheritance chain, which reduces
overhead slightly.

Source/Core/AudioCommon/WaveFile.cpp

@@ -147,7 +147,7 @@ void WaveFileWriter::AddStereoSamplesBE(const short* sample_data, u32 count, int
   {
     Stop();
     file_index++;
-    std::stringstream filename;
+    std::ostringstream filename;
     filename << File::GetUserPath(D_DUMPAUDIO_IDX) << basename << file_index << ".wav";
     Start(filename.str(), sample_rate);
     current_sample_rate = sample_rate;

Source/Core/Common/Debug/Watches.cpp

@@ -104,7 +104,7 @@ std::vector<std::string> Watches::SaveToStrings() const
   std::vector<std::string> watches;
   for (const auto& watch : m_watches)
   {
-    std::stringstream ss;
+    std::ostringstream ss;
     ss << std::hex << watch.address << " " << watch.name;
     watches.push_back(ss.str());
   }

Source/Core/Common/StringUtil.cpp

@@ -398,7 +398,7 @@ std::string JoinStrings(const std::vector<std::string>& strings, const std::stri
   if (strings.empty())
     return "";
 
-  std::stringstream res;
+  std::ostringstream res;
   std::copy(strings.begin(), strings.end(),
             std::ostream_iterator<std::string>(res, delimiter.c_str()));
 

Source/Core/Core/HW/SI/SI.cpp

@@ -307,7 +307,7 @@ static void RunSIBuffer(u64 user_data, s64 cycles_late)
               s_com_csr.CHANNEL, request_length, expected_response_length, actual_response_length);
     if (expected_response_length != actual_response_length)
     {
-      std::stringstream ss;
+      std::ostringstream ss;
       for (u8 b : request_copy)
       {
         ss << std::hex << std::setw(2) << std::setfill('0') << (int)b << ' ';

Source/Core/Core/IOS/USB/Bluetooth/BTReal.cpp

@@ -512,7 +512,7 @@ void BluetoothReal::LoadLinkKeys()
     for (size_t i = 0; i < key_string.length(); i = i + 2)
     {
       int value;
-      std::stringstream(key_string.substr(i, 2)) >> std::hex >> value;
+      std::istringstream(key_string.substr(i, 2)) >> std::hex >> value;
       key[pos++] = value;
     }
 

Source/Core/Core/IOS/USB/OH0/OH0Device.cpp

@@ -18,7 +18,7 @@ namespace IOS::HLE::Device
 {
 static void GetVidPidFromDevicePath(const std::string& device_path, u16& vid, u16& pid)
 {
-  std::stringstream stream{device_path};
+  std::istringstream stream{device_path};
   std::string segment;
   std::vector<std::string> list;
   while (std::getline(stream, segment, '/'))

Source/Core/Core/MemoryWatcher.cpp

@@ -50,7 +50,7 @@ void MemoryWatcher::ParseLine(const std::string& line)
   m_values[line] = 0;
   m_addresses[line] = std::vector<u32>();
 
-  std::stringstream offsets(line);
+  std::istringstream offsets(line);
   offsets >> std::hex;
   u32 offset;
   while (offsets >> offset)
@@ -76,7 +76,7 @@ u32 MemoryWatcher::ChasePointer(const std::string& line)
 
 std::string MemoryWatcher::ComposeMessages()
 {
-  std::stringstream message_stream;
+  std::ostringstream message_stream;
   message_stream << std::hex;
 
   for (auto& entry : m_values)

Source/Core/Core/Movie.cpp

@@ -185,7 +185,7 @@ std::string GetRTCDisplay()
   const time_t current_time = CEXIIPL::GetEmulatedTime(CEXIIPL::UNIX_EPOCH);
   const tm* const gm_time = gmtime(&current_time);
 
-  std::stringstream format_time;
+  std::ostringstream format_time;
   format_time << std::put_time(gm_time, "Date/Time: %c\n");
   return format_time.str();
 }

Source/Core/Core/PowerPC/BreakPoints.cpp

@@ -37,7 +37,7 @@ BreakPoints::TBreakPointsStr BreakPoints::GetStrings() const
   {
     if (!bp.is_temporary)
     {
-      std::stringstream ss;
+      std::ostringstream ss;
       ss << std::hex << bp.address << " " << (bp.is_enabled ? "n" : "");
       bp_strings.push_back(ss.str());
     }
@@ -130,7 +130,7 @@ MemChecks::TMemChecksStr MemChecks::GetStrings() const
   TMemChecksStr mc_strings;
   for (const TMemCheck& mc : m_mem_checks)
   {
-    std::stringstream ss;
+    std::ostringstream ss;
     ss << std::hex << mc.start_address;
     ss << " " << (mc.is_ranged ? mc.end_address : mc.start_address) << " "
        << (mc.is_ranged ? "n" : "") << (mc.is_break_on_read ? "r" : "")

Source/Core/Core/PowerPC/Jit64/Jit.cpp

@@ -1193,7 +1193,7 @@ void LogGeneratedX86(size_t size, const PPCAnalyst::CodeBuffer& code_buffer, con
 
   if (b->codeSize <= 250)
   {
-    std::stringstream ss;
+    std::ostringstream ss;
     ss << std::hex;
     for (u8 i = 0; i <= b->codeSize; i++)
     {

Source/Core/UICommon/UICommon.cpp

@@ -464,7 +464,7 @@ std::string FormatSize(u64 bytes)
 
   // Don't need exact values, only 5 most significant digits
   const double unit_size = std::pow(2, unit * 10);
-  std::stringstream ss;
+  std::ostringstream ss;
   ss << std::fixed << std::setprecision(2);
   ss << bytes / unit_size << ' ' << Common::GetStringT(unit_symbols[unit]);
   return ss.str();

Source/Core/VideoCommon/PostProcessing.cpp

@@ -434,7 +434,7 @@ void PostProcessing::BlitFromTexture(const MathUtil::Rectangle<int>& dst,
 
 std::string PostProcessing::GetUniformBufferHeader() const
 {
-  std::stringstream ss;
+  std::ostringstream ss;
   u32 unused_counter = 1;
   if (g_ActiveConfig.backend_info.api_type == APIType::D3D)
     ss << "cbuffer PSBlock : register(b0) {\n";
@@ -493,7 +493,7 @@ std::string PostProcessing::GetUniformBufferHeader() const
 
 std::string PostProcessing::GetHeader() const
 {
-  std::stringstream ss;
+  std::ostringstream ss;
   ss << GetUniformBufferHeader();
   if (g_ActiveConfig.backend_info.api_type == APIType::D3D)
   {
@@ -602,7 +602,7 @@ void main(in float3 v_tex0_ : TEXCOORD0, out float4 ocol0_ : SV_Target)
 
 bool PostProcessing::CompileVertexShader()
 {
-  std::stringstream ss;
+  std::ostringstream ss;
   ss << GetUniformBufferHeader();
 
   if (g_ActiveConfig.backend_info.api_type == APIType::D3D)

Source/Core/VideoCommon/TextureConversionShader.cpp

@@ -1392,7 +1392,7 @@ std::string GenerateDecodingShader(TextureFormat format, TLUTFormat palette_form
   if (!info)
     return "";
 
-  std::stringstream ss;
+  std::ostringstream ss;
   switch (palette_format)
   {
   case TLUTFormat::IA8:
@@ -1414,7 +1414,7 @@ std::string GenerateDecodingShader(TextureFormat format, TLUTFormat palette_form
 
 std::string GeneratePaletteConversionShader(TLUTFormat palette_format, APIType api_type)
 {
-  std::stringstream ss;
+  std::ostringstream ss;
 
   ss << R"(
 int Convert3To8(int v)

Source/Core/VideoCommon/VertexManagerBase.cpp

@@ -768,12 +768,12 @@ void VertexManagerBase::OnEndFrame()
 
 #if 0
   {
-    std::stringstream ss;
+    std::ostringstream ss;
     std::for_each(m_cpu_accesses_this_frame.begin(), m_cpu_accesses_this_frame.end(), [&ss](u32 idx) { ss << idx << ","; });
     WARN_LOG(VIDEO, "CPU EFB accesses in last frame: %s", ss.str().c_str());
   }
   {
-    std::stringstream ss;
+    std::ostringstream ss;
     std::for_each(m_scheduled_command_buffer_kicks.begin(), m_scheduled_command_buffer_kicks.end(), [&ss](u32 idx) { ss << idx << ","; });
     WARN_LOG(VIDEO, "Scheduled command buffer kicks: %s", ss.str().c_str());
   }