[tint][spirv-writer] Add a KeepBindingArrayAsPointer transform.

KeepBindingArrayAsPointer is a transform that ensures that binding_arrays
are never stored by value but only used via a pointer to them. This is
used to produce SPIR-V that's more similar to what drivers typically
ingest where OpTypeArray<OpTypeImage> is always kept as a pointer.

Note that it doesn't handle function parameters so DirectVariableAccess
(DVA) for handles must have run prior to this transform.

This mismatch between Tint IR and SPIR-V at the time of writing is
because Tint IR disallows handle address space pointers as function
arguments, while "idiomatic" SPIR-V that drivers are used to use pointers
to pass handle types as function arguments.

Bug: 393558555
Change-Id: I2a37899b938dd773a6d991d6ebf58f30a3a6a5ca
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/247054
Reviewed-by: James Price <jrprice@google.com>
Auto-Submit: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>