WGSL: Cannot alias u32, vec3f, and other previously reserved words

[stefnotch]

Description

u32, vec3f and other types are no longer reserved keywords in WGSL. They're predeclared types.

So aliasing them should be valid, even if very odd.

Repro steps
Add the following test to naga\src\front\wgsl\tests.rs

#[test]
fn parse_alias_builtin() {
    parse_str(
        "
        alias u32 = i32;
        alias vec2f = vec3f;
        fn main1() {
            var x: u32 = -1i;
            var y: vec2f = vec3<f32>(1.0, 2.0, 3.0);
        }
    ",
    )
    .unwrap();

    parse_str(
        "
        alias u32 = i32;
        alias vec2f = vec3f;
        struct Foo { x: u32, y: vec2f }
        fn main() {
            var x: Foo = Foo(-1i, vec3<f32>(1.0, 2.0, 3.0));
        }
    ",
    )
    .unwrap();
}

Expected vs observed behavior
I expected the shaders to compile. Actual behaviour is that it fails with

thread 'front::wgsl::tests::parse_alias_builtin' panicked at naga\src\front\wgsl\tests.rs:150:6:
called `Result::unwrap()` on an `Err` value: ParseError { message: "name `u32` is a reserved keyword", labels: [(Span { start: 15, end: 18 }, "definition of `u32`")], notes: [] }

Extra materials
This may be related to #4473 ?

Platform

• Windows 11
• WGSL trunk on commit 583cc6a (one of the latest commits)

[teoxoy]

#4406 should cover this but we can keep this open as I'm not sure what's left to do and this seems like a subtask.

[stefnotch]

Good to know that this is a duplicate of an existing issue, thank you for finding it!