Vulkan: Fix a few framebuffer fetch bugs A few fixes to framebuffer fetch: - The built-in symbol for coherent and non-coherent are now the same for gl_LastFragData, so extension check can choose one or the other. - The temporary variable used in a transformation is renamed to not be gl_LastFragData. - inout usage is now validated correctly for shader type and version. Bug: angleproject:6951 Bug: angleproject:6905 Bug: angleproject:6907 Change-Id: I9af341a3e8e01ed375a8230618184494813d3ece Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3427577 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>