Rollup merge of #71610 - divergentdave:InvalidUndefBytes-range, r=RalfJung

Rollup merge of #71610 - divergentdave:InvalidUndefBytes-range, r=RalfJung

InvalidUndefBytes: Track size of undef region used

This PR adds a size to `UndefinedBehaviorInfo::InvalidUndefBytes`, to keep track of how many undefined bytes in a row were accessed, and changes a few methods to pass this information through. This additional information will eventually be used in Miri to improve diagnostics for this UB error. See also rust-lang/miri#1354 for prior discussion.

I expect Miri will break the next time its submodule is updated, due to this change to the `InvalidUndefBytes`. (The current commit for src/tools/miri predates rust-lang/miri#1354, and thus does not try to destructure the `InvalidUndefBytes` variant) I have a corresponding change prepared for that repository.

r? @RalfJung