[naga spv-in] Add support for memory barriers

[PhenaOfMari]

Description
Naga's SpirV ingest currently has support for control barriers, but not memory-only barriers. This PR endeavors to add this support for SpirV in as well as any language out that may make proper use of them. Languages that don't support memory barriers without an execution barrier will follow the existing Control Barrier path.

Additionally, Control Barriers for SpirV in and out have no distinction between workgroup and subgroup memory scopes. Support for that has been added as a separate commit, which can easily be pulled out into a separate pull request if desired.

Testing
I've compiled a simple shader with rust-gpu that utilizes their memory_barrier function. These changes allow the compiled shader to be parsed and executed, where previously the validator would panic that OpMemoryBarrier was unsupported. I've also added a spvasm file to naga/tests/in/spv that compiles to all backends.

Squash or Rebase
Both commits should be able to stand on their own if whoever does the merge prefers to rebase. Either way is fine.

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests. If applicable, add:
  • --target wasm32-unknown-unknown
• Run cargo xtask test to run tests.
• If this contains user-facing changes, add a CHANGELOG.md entry.

[LegNeato]

This looks great, can't wait for it to land!

[teoxoy]

Looks good overall!