Vulkan 1.1 section 15.3.5 table 24 specifies "Conversion to RGBA"
to use 'one' as the last component when it's not present in the format,
where "one = 1.0f for floating-point formats and depth aspects, and
one = 1 for integer formats and stencil aspects", and 0 for the other
missing components.

Bug b/129523279

Change-Id: I9e4b0b9a8d1d696e51fc76b6554045835966c4b0
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/29274
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>