This will be used by OpCompositeInsert and OpCompositeExtract. All
indices are known at compile time, and are specified as literals rather
than ids of constants, (as in Op*AccessChain)

Bug: b/126475423
Change-Id: Ic29e2f988fb6b9bdab4b722b368e51db929c8bd3
Reviewed-on: https://swiftshader-review.googlesource.com/c/25213Tested-by: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>