Test for overflow conditions in validation involving offsets and sizes

[ErichDonGubler]

Validation in CTS tends to do a good job of covering edge cases for limits. We in Firefox have noticed that CTS' validation generally doesn't try to cover edge cases for the bounds of integral values, and this seems interesting to add. This is valuable because:

1. Obviously, validation of bounds always needs to be robust for these edge cases.
2. Less obviously, rendered diagnostics should also not encounter overflow.

Adding coverage for (1) is essential for ensuring that an implementation safely handles inputs, independent of things like maximum values for limits. (2) is nice, and generally comes for free with (1).

JS doesn't tend to give direct access to overflow cases for GPUSize64s, but this seems achievable with APIs that accept GPUSize32s offsets and sizes.

[kainino0x]

GPUSize64 ([EnforceRange] unsigned long long) does throw exceptions for numbers outside [0, Number.MAX_SAFE_INTEGER].

These would go in the idl directory and the reason we haven't done this is that they're defined by the WebIDL spec and I felt reasonably safe in assuming browsers' WebIDL implementations were correct, so WebGPU implementations would get it right as long as they followed the WebIDL code from the spec. See #332