[wgpu-types]: Add cross-platform Mutex and RwLock

[bushrat011899]

Connections

• Contributes to Support no_std where possible (specifically for wasm32v1-none) #6826
• Based on MVP no_std for wgpu-core #7746

Description

Across Wgpu's various crates there is a need for locking primitives, such as Mutex and RwLock. Currently, each crate independently imports from either std, parking_lot, or potentially uses a RefCell-based fallback for no_std compatibility. This leads to duplicated implementations of the fallback logic. This PR centralizes these Mutex and RwLock definitions into wgpu-types, allowing them to be re-used across Wgpu. Note that while that is the intention of this PR, currently it just adds the types to wgpu-types; it does not switch the various crates to it. I consider this to be a reasonable split to reduce merge conflicts while the design is reviewed.

Testing

• CI

Squash or Rebase?

• Rebase

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.