[naga] Enforce a maximum array size

[andyleiserson]

We should enforce a maximum array size. Places where this might matter:

• In the bounds-checking implementation, we are casting between signed and unsigned integers, which implies we may be indexing arrays with signed integers, which would imply a maximum array size of 2^31.
• The function TypeInner::size returns the size of a type in a u32, which implies a maximum byte size of any array. WGSL attempt to multiply with overflow due to large array #4339 reports an overflow error here due to a large array.

gpuweb#2118 discussed, and gpuweb#3078 set, a limit on array size, although the current spec has different language about the maximum amount of data accessed by a function or shader.