StringUtil: Move IsAlpha() into Common namespace

Source/Core/Common/StringUtil.h

@@ -238,14 +238,6 @@ inline bool IsPrintableCharacter(char c)
   return std::isprint(c, std::locale::classic());
 }
 
-/// Returns whether a character is a letter, i.e. whether 'a' <= c <= 'z' || 'A' <= c <= 'Z'
-/// is true. Use this instead of calling std::isalpha directly to ensure
-/// the C locale is being used and to avoid possibly undefined behaviour.
-inline bool IsAlpha(char c)
-{
-  return std::isalpha(c, std::locale::classic());
-}
-
 #ifdef _WIN32
 std::vector<std::string> CommandLineToUtf8Argv(const wchar_t* command_line);
 #endif
@@ -254,14 +246,24 @@ std::string GetEscapedHtml(std::string html);
 
 namespace Common
 {
+/// Returns whether a character is a letter, i.e. whether 'a' <= c <= 'z' || 'A' <= c <= 'Z'
+/// is true. Use this instead of calling std::isalpha directly to ensure
+/// the C locale is being used and to avoid possibly undefined behaviour.
+inline bool IsAlpha(char c)
+{
+  return std::isalpha(c, std::locale::classic());
+}
+
 inline char ToLower(char ch)
 {
   return std::tolower(ch, std::locale::classic());
 }
+
 inline char ToUpper(char ch)
 {
   return std::toupper(ch, std::locale::classic());
 }
+
 void ToLower(std::string* str);
 void ToUpper(std::string* str);
 bool CaseInsensitiveEquals(std::string_view a, std::string_view b);

Source/Core/InputCommon/ControllerInterface/MappingCommon.cpp

@@ -43,7 +43,7 @@ std::string GetExpressionForControl(const std::string& control_name,
   {
     // If our expression contains any non-alpha characters
     // we should quote it
-    if (!std::all_of(expr.begin(), expr.end(), IsAlpha))
+    if (!std::all_of(expr.begin(), expr.end(), Common::IsAlpha))
       expr = fmt::format("`{}`", expr);
   }