wgsl: limit layout size of a type #2118

Example:

         var<private> a : array<f32, 0x40000000>;      // 4 billion-ish byte big.

A similar thing can happen with a bigger element type but fewer of them.

Also

       struct S {
            [[size(0xfffffffc)]] a: i32; 
            b: i32;  // byte offset overflows 32-bit
       };

We'd like to be able to reject programs with data structures that are "too big", i.e. have overflowing sizes.

We already visited this somewhat in the max-array-size discussion, and I recall the judgement being "an implementation can reject unreasonably sized arrays", and nothing was added to the spec about that.

So these are two more cases that may fall into the same case.

There are at least a couple of options:

• Call things like this a "spurious error" (See can pipeline creation fail in the driver compiler? particularly due to shader compilation failure #1872), or
• Add another few cases to [wgsl] Limit number of function parameters to 255 #1959 (add a limits section)

cc: @ben-clayton