This allows `wgpu` to not unconditionally depend on `std::path::Path`.
It’s also, in my opinion, more user-friendly, because the feature which
most users will not use (and is not currently functional) is now a
defaultable struct field instead of a required parameter.
The disadvantage is that `wgpu-types` now has to know about tracing.
Makes the dual source implementation in wgpu WebGPU spec compliant.
Furthermore, makes the dual source blending extension available when targeting WebGPU.
When the user provides values for a module's overrides, rather than
replacing override-sized array types with ordinary array types (which
could require adjusting type handles throughout the module), instead
edit all overrides to have initializers that are fully-evaluated
constant expressions. Then, change all backends to handle
override-sized arrays by retrieving their overrides' values.
For arrays whose sizes are override expressions, not simple references
to a specific override's value, let front ends built array types that
refer to anonymous overrides whose initializers are the necessary
expression.
This means that all arrays whose sizes are override expressions are
references to some `Override`. Remove `naga::PendingArraySize`, and
let `ArraySize::Pending` hold a `Handle<Override>` in all cases.
Expand `tests/gpu-tests/shader/array_size_overrides.rs` to include the
test case that motivated this approach.
