* add GL_EXT_texture_shadow_lod feature detection
* allow more cases of cube depth texture sampling in glsl
* add test for sampling a cubemap array depth texture with lod
* add test for chosing GL_EXT_texture_shadow_lod over the grad workaround if instructed
* add changelog entry for GL_EXT_texture_shadow_lod
* fix criteria for requiring and using TEXTURE_SHADOW_LOD
* require gles 320 for textureSampling over cubeArrayShadow
* prevent false positives in TEXTURE_SHADOW_LOD in checks
* make workaround_lod_with_grad usecase selection less context dependant
* move 3d array texture error into the validator
* correct ImageSample logic errors
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.
Add an `I64` variant to `crate::Literal`, making `crate::Expression`
suitable for representing `AbstractFloat` and `AbstractInt` values in
the WGSL front end.
Make validation reject uses of `Literal::I64` in constant and function
expression arenas unconditionally. Add tests for this.
Let the frontends and backends for languages that have 64-bit integers
read/write them.
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.
