Support RuntimeDescriptorArray when ingesting SPIR-V

[hasenbanck]

While testing "slang" as a shader language, I produced SPIR-V that contained unbound texture arrays (for which I would write a binding array in WGSL):

[[vk::binding(0, 2)]]
Texture2D textures[];

// WGSL equivelent:
// @group(2) @binding(0) var textures: binding_array<texture_2d<f32>>;

When compiling the shader with this SPIR-V using the include_spirv!() macro, I get the following validation error:

parsing error: UnsupportedCapability(RuntimeDescriptorArray)

It would be great if naga could ingest SPIR-V that use runtime descriptor arrays.

PS: When bounding the txture array, naga will happily accept the SPIR-V and wgpu will run the shader. Since it seems that wgpu does not properly do bounds checking, the shader will work as if it was boundless (which could be seens as kind of a workaround).

[cwfitzgerald]

What wgpu version - I just tested adding that cap on trunk and it works fine. I do get a different error though