Naga should require Capabilities to accept binding_array types at all

[jimblandy]

Naga accepts binding_array as a type, even with no Capabilities flags set that would allow it to be used. For use in WebGPU, Naga should not even allow such variables to be declared.

For example, Firefox accepts the following shader module:

@group(0) @binding(0) var<uniform> big_xform: mat2x2<f32>;
@group(0) @binding(1) var<uniform> small_xform: mat2x2<f32>;
@group(0) @binding(2) var ba: binding_array<texture_2d<f32>>;

@vertex
fn vertex_shader(@location(0) center: vec2<f32>,
                 @location(1) corner: vec2<f32>)
                 -> @builtin(position) vec4<f32>
{
   let pos = big_xform * center + small_xform * corner;
   return vec4<f32>(pos.x, pos.y, 0.0, 1.0);
}

@fragment
fn blue() -> @location(0) vec4<f32> {
   return vec4<f32>(0.0, 0.0, 1.0, 1.0);
}

[teoxoy]

Related: #4407