It is typical for apps to have many image views (and buffer views) with
the same parameters. This change avoids generating new sampling routines
for image views with identical state.

The vk::Identifier class compresses the state into a 32-bit value that
is used as part of the key for the sampling routine cache.

Bug: b/151235334
Change-Id: I00fc19a91639803273d0f7d6b9fed9fc5b481898
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/42388
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>