This makes Naga IR validation impose the restrictions added to WGSL in
gpuweb/gpuweb#1801.
Remove code in the SPIR-V writer to spill arrays to temporary variables in order
to index them dynamically. If such IR is encountered, treat it as a failure of
validation.
Better errors for Unexpected, BadInteger, BadFloat, BadTexture, BadTypeCast, UnknownScalarType, UnknownStorageClass, UnknownAttribute, UnknownBuiltin, UnknownShaderStage, UnknownStorageFormat and UnknownConservativeDepth, ZeroStride, ZeroSizeOrAlign and UnknownType.
Also adds lexer::capture_span.
Also fixes some validation for texture sample types and and issue that cauld cause e.g. the type `f33` to be parsed as `f32`.
The `apply_common_default_interpolation` helper function would panic if bindings
were missing, but missing bindings should be something that front ends can count
on validation to detect, so the helper should just return silently.
The validator returned `InvalidType` errors for missing bindings, apparently
because variables without bindings must be structs that do have bindings. But
this is unhelpful when you've just forgotten to label an argument. So this patch
adds a new, more specific, `VaryingError` variant.
This lets us reduce noise by removing a bunch of `#[cfg]` attributes. In the
future, if we have tests for other front ends, we can create an `errors`
subdirectory, but for now, we only have the WGSL tests, so we should keep things
flat.
