[naga const-eval] LiteralVector and some demo builtins

[sagudev]

Connections
Continuation of #6213.
Implements some functions in const #4507.

Description
Existing macros work for component-wise cases where return type is equal to input type. But it's hard to generalize macros further. So I present LiteralVector:

/// Vector for each [`Literal`] type
///
/// This type ensures that all elements have same type
enum LiteralVector {
    F64(ArrayVec<f64, { crate::VectorSize::MAX }>),
    F32(ArrayVec<f32, { crate::VectorSize::MAX }>),
    U32(ArrayVec<u32, { crate::VectorSize::MAX }>),
    I32(ArrayVec<i32, { crate::VectorSize::MAX }>),
    U64(ArrayVec<u64, { crate::VectorSize::MAX }>),
    I64(ArrayVec<i64, { crate::VectorSize::MAX }>),
    Bool(ArrayVec<bool, { crate::VectorSize::MAX }>),
    AbstractInt(ArrayVec<i64, { crate::VectorSize::MAX }>),
    AbstractFloat(ArrayVec<f64, { crate::VectorSize::MAX }>),
}

that abstracts away at least vector obtaining logic. This makes it easier to implement some builtins that needs access to all components like dot, length, distance (folds LiteralVector to Literal) and normalize (maps LiteralVector).

Testing
There are some snapshot tests.

Squash or Rebase?
Reviewable per commit.
Squash

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.

[ErichDonGubler]

nitpick: IMO it'd have been better to have this refactor separated for the purpose of review, but 🤷🏻‍♂️ it's not too hard to follow.

[ErichDonGubler]

Review TODO for myself: figure out what the "zero vector" domain exception listed in the standard is, and see if we need to validate it out.

[sagudev]

Relevant spec parts https://www.w3.org/TR/WGSL/#normalize-builtin:

The domain is all vectors except the zero vector.

and

When evaluated outside its domain, the default exception handling rules of IEEE-754 require an implementation to generate an exception and yield a NaN value. In contrast, WGSL does not mandate floating point exceptions, and may instead yield an indeterminate value. See § 15.7.2 Differences from IEEE-754.

So we can do anything we want, current code will return NaN.

[ErichDonGubler]

Just wanted to acknowledge that I'm taking a long time to finish this review. I haven't had bandwidth to spare, with some Mozilla tasks overriding my other priorities. I'm hoping to get to this early next week! ❤️💦