Adds UAV support for D3D12, Vulkan and reworked for OpenGL, D3D11 (#2119)

* Adds UAV support for D3D12, Vulkan and reworked support for OpenGL, D3D11

UAV support is now uniform across compute and draw.
To set a UAV you just use bgfx::setImage() and IMAGE2D in the shader, just like in compute.
Due to these changes shaders will have to be recompiled.

The changes include:
	- D3D11 requires patching of the UAV slot number (which is now done by modifying the DXBC instead of using a macro)
	- If the DXBC binary includes a debug chunk, that is also patched to match the new slot number
	- All the other renderers don't need any kind of patching
	- There are some shader annotations to better convert the UAV format used in hlsl to spirv

Possibility of further enhancements:
	- bgfx::setViewFrameBuffer() only supports binding to a framebuffer or, using BGFX_INVALID_HANDLE, to bind the default backbuffer. This doesn't allow for the case where there is no need to bind to either one of them, for example when using a fragment shader only to read and write to an UAV.

* Bump shader version, because they need to be recompiled.

tools/shaderc/shaderc_spirv.cpp

@@ -1023,7 +1023,7 @@ namespace bgfx { namespace spirv
 						}
 					}
 
-					// Loop through the separate_images, and extract the uniform names:
+					// Loop through the storage_images, and extract the uniform names:
 					for (auto &resource : resourcesrefl.storage_images)
 					{
 						std::string name = refl.get_name(resource.id);