VideoCommon/BoundingBox: Move PixelShaderManager::SetBoundingBoxActive() calls into Enable()/Disable()

Now that we have an actual interface to manage things, we can stop
duplicating the calls to to the pixel shader manager and remove the
need to remember to actually do so when disabling or enabling the
bounding box.

Source/Core/VideoCommon/BPStructs.cpp

@@ -278,9 +278,7 @@ static void BPWritten(const BPCmd& bp)
       // We should be able to get away with deactivating the current bbox tracking
       // here. Not sure if there's a better spot to put this.
       // the number of lines copied is determined by the y scale * source efb height
-
       BoundingBox::Disable();
-      PixelShaderManager::SetBoundingBoxActive(false);
 
       float yScale;
       if (PE_copy.scale_invert)
@@ -450,7 +448,6 @@ static void BPWritten(const BPCmd& bp)
   {
     const u8 offset = bp.address & 2;
     BoundingBox::Enable();
-    PixelShaderManager::SetBoundingBoxActive(true);
 
     if (g_ActiveConfig.backend_info.bSupportsBBox && g_ActiveConfig.bBBoxEnable)
     {

Source/Core/VideoCommon/BoundingBox.cpp

@@ -9,6 +9,7 @@
 
 #include "Common/ChunkFile.h"
 #include "Common/CommonTypes.h"
+#include "VideoCommon/PixelShaderManager.h"
 
 namespace BoundingBox
 {
@@ -29,11 +30,13 @@ std::array<u16, 4> s_coordinates{
 void Enable()
 {
   s_is_active = true;
+  PixelShaderManager::SetBoundingBoxActive(s_is_active);
 }
 
 void Disable()
 {
   s_is_active = false;
+  PixelShaderManager::SetBoundingBoxActive(s_is_active);
 }
 
 bool IsEnabled()

Source/Core/VideoCommon/PixelEngine.cpp

@@ -19,7 +19,6 @@
 #include "VideoCommon/BoundingBox.h"
 #include "VideoCommon/Fifo.h"
 #include "VideoCommon/PerfQueryBase.h"
-#include "VideoCommon/PixelShaderManager.h"
 #include "VideoCommon/VideoBackendBase.h"
 
 namespace PixelEngine
@@ -234,7 +233,6 @@ void RegisterMMIO(MMIO::Mapping* mmio, u32 base)
   {
     mmio->Register(base | (PE_BBOX_LEFT + 2 * i), MMIO::ComplexRead<u16>([i](u32) {
                      BoundingBox::Disable();
-                     PixelShaderManager::SetBoundingBoxActive(false);
                      return g_video_backend->Video_GetBoundingBox(i);
                    }),
                    MMIO::InvalidWrite<u16>());