Add a per-shader debuggable flag to allow finer grained status

* E.g. on D3D12 we can debug DXBC shaders but not DXIL shaders. On vulkan this
  will allow us to have the UI work better when encountering shaders with
  unsupported capabilities or extensions.

renderdoc/api/replay/shader_types.h

@@ -1269,6 +1269,17 @@ The first entry in the list is always the file where the entry point is.
 
   DOCUMENT("The :class:`ShaderEncoding` of the source. See :data:`files`.");
   ShaderEncoding encoding = ShaderEncoding::Unknown;
+
+  DOCUMENT(R"(Indicates whether this particular shader can be debugged. In some cases even if the
+API can debug shaders in general, specific shaders cannot be debugged because they use unsupported
+functionality
+)");
+  bool debuggable = true;
+
+  DOCUMENT(R"(If :data:`debuggable` is false then this contains a simple explanation of why the
+shader is not supported for debugging
+)");
+  rdcstr debugStatus;
 };
 
 DECLARE_REFLECTION_STRUCT(ShaderDebugInfo);