tint: Implement const-eval of quantizeToF16
Bug: tint:1581
Change-Id: I5cf9806bde7875282d3b67731dbb88666523f598
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/108142
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>