Add special resource type for A8_UNORM. Closes #1426

* While it's redundant this format is still valid in D3D so needs to be handled
  correctly.

renderdoc/api/replay/renderdoc_tostr.inl

@@ -101,6 +101,8 @@ rdcstr DoStringise(const ResourceFormatType &el)
     STRINGISE_ENUM_CLASS(YUV10);
     STRINGISE_ENUM_CLASS(YUV12);
     STRINGISE_ENUM_CLASS(YUV16);
+    STRINGISE_ENUM_CLASS(PVRTC);
+    STRINGISE_ENUM_CLASS(A8);
   }
   END_ENUM_STRINGISE();
 }

renderdoc/api/replay/replay_enums.h

@@ -1312,6 +1312,10 @@ or formats that don't have equal byte-multiple sizes for each channel.
 .. data:: PVRTC
 
   PowerVR properitary texture compression format.
+
+.. data:: A8
+
+  8-bit unsigned normalised alpha - equivalent to standard R8 with a pre-baked swizzle.
 )");
 enum class ResourceFormatType : uint8_t
 {
@@ -1343,6 +1347,7 @@ enum class ResourceFormatType : uint8_t
   YUV12,
   YUV16,
   PVRTC,
+  A8,
 };
 
 DECLARE_REFLECTION_ENUM(ResourceFormatType);