VkPipelineMultisampleStateCreateInfo contains parameters specific
to the sampleRateShading feature. This cl handles these new
parameters (without enabling the sampleRateShading feature).

Bug: b/171415086
Change-Id: I8e895483ab5d27643a2fc59347bb41a51570602d
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/51732Tested-by: Alexis Hétu <sugoi@google.com>
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>