This is a step toward being able to claim support for
storageImageExtendedFormats.

Bug: b/146579770
Test: dEQP-VK.*r16g16*
Change-Id: Iba658f39271f7e181c10c117e53c8e3dbdf37595
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/39769
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Chris Forbes <chrisforbes@google.com>