This Cl adds the ability to clone a constant into a context provided.
This allows the IR to clone the constants out of the Program and into
the IR.
Bug: tint:1718
Change-Id: I78170cdc66b5824a1ab81000976a747b5bffee79
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/116363
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>