Have `compact::compact` preserve entries in the `Module::types` arena
if they have names.
Future abstract type support will require the WGSL front end to
compact the module before validation. Without this change, that will
drop `alias` declarations, making it harder to test type validation.
Previously, implicit padding members of `struct`s were suppressed from
structure definitions in Metal output if they had a binding specified
for them (i.e., `@location(0)`). This padding is, however, is necessary
for correct access of member fields passed into shaders by uniform and
storage buffers. Unconditionally emit padding members for `struct`s.
Resolves
[`gfx-rs/wgpu`#4701](https://github.com/gfx-rs/wgpu/pull/4701).
Let `naga::TypeInner::Matrix` hold a full `Scalar`, with a kind and
byte width, not merely a byte width, to make it possible to represent
matrices of AbstractFloats for WGSL.
When asked to evaluate an `Expression::As` cast applied to a `Splat`
expression, change `ConstantEvaluator::cast` to preserve the `Splat`,
rather than expanding it out to a `Compose` expression.
Introduce a new struct type, `Scalar`, combining a `ScalarKind` and a
`Bytes` width, and use this whenever such pairs of values are passed
around.
In particular, use `Scalar` in `TypeInner` variants `Scalar`, `Vector`,
`Atomic`, and `ValuePointer`.
Introduce associated `Scalar` constants `I32`, `U32`, `F32`, `BOOL`
and `F64`, for common cases.
Introduce a helper function `Scalar::float` for constructing `Float`
scalars of a given width, for dealing with `TypeInner::Matrix`, which
only supplies the scalar width of its elements, not a kind.
Introduce helper functions on `Literal` and `TypeInner`, to produce
the `Scalar` describing elements' values.
Use `Scalar` in `wgpu_core::validation::NumericType` as well.
