Add shader I64 and U64 support

[atlv24]

Connections Part of an incoming series of PRs needed by #5123 Others in this series: #5155 Addresses #4424 Ultimately for bevy meshlets pipeline https://github.com/bevyengine/bevy/pull/10164

Description Shaders currently do not support 64 bit integer types. Add support for these gated by a feature flag when the capability is present.

Testing A snapshot test called i64.wgsl has been added to test parsing, type casting, and other basic operations.

Checklist

• [x] Run cargo fmt.
• [x] Run cargo clippy. If applicable, add:
  • [ ] --target wasm32-unknown-unknown
  • [ ] --target wasm32-unknown-emscripten
• [x] Run cargo xtask test to run tests.
• [x] Add change to CHANGELOG.md. See simple instructions inside file.