This fixes operators in wasm Turbofan that were mixing up integer sizes
and pointers with tagged pointers.

Additional changes:
- Remove unused (and non-compiling if V8_MAP_PACKING)
  GraphAssembler::StoreMap.
- Factor out WasmGraphBuilder::IsNull.

Change-Id: I9d99827e35507adc0af391bd39975d55371b98cf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3306981Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78196}