Refactor custom shaders to abstract binding differences. Closes #2458

* Newly written shaders and any updated shaders can now use pre-defined macros
  to abstract away binding differences between APIs, so custom shaders will be
  more portable in particular shaders written in HLSL for D3D or GLSL on OpenGL
  won't break on vulkan because they refer to incorrect binds.

qrenderdoc/Windows/TextureViewer.cpp

@@ -4246,7 +4246,8 @@ void TextureViewer::reloadCustomShaders(const QString &filter)
 
         bytebuf shaderBytes(source.toUtf8());
 
-        rdcarray<ShaderEncoding> supported = m_Ctx.TargetShaderEncodings();
+        rdcarray<ShaderEncoding> supported = m_Ctx.CustomShaderEncodings();
+        rdcarray<ShaderSourcePrefix> prefixes = m_Ctx.CustomShaderSourcePrefixes();
 
         rdcstr errors;
 
@@ -4258,6 +4259,16 @@ void TextureViewer::reloadCustomShaders(const QString &filter)
             // pick the first tool that can convert to an accepted format
             if(tool.input == encoding && supported.contains(tool.output))
             {
+              // apply any prefix needed
+              for(const ShaderSourcePrefix &prefix : prefixes)
+              {
+                if(prefix.encoding == encoding)
+                {
+                  source = QString(prefix.prefix) + source;
+                  break;
+                }
+              }
+
               ShaderToolOutput out =
                   tool.CompileShader(this, source, "main", ShaderStage::Pixel, "");