[SkSLC] Enable ForceNoRTFlip for WGSL

When running skslc in debug mode, an assert
(https://source.chromium.org/chromium/chromium/src/+/main:third_party/skia/src/sksl/codegen/SkSLWGSLCodeGenerator.cpp;l=3267;drc=dd26c181cbe834ae5d1cdc37677ce03df064a1bc)
would trigger for WGSL, enable ForceNoRTFlip to satisfy the assumption
that this setting will always be true with only Graphite using WGSL.

Change-Id: I31d1ea9dd7e2fb4c12ad71fb95e733370428e89e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1293836
Commit-Queue: Nathan Sanchez <nathanasanchez@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>