Fix explicit layout validator memory alloc problems (#56757)

Fix explicit layout validator memory alloc problems (#56757)

The ExplicitLayoutValidator currently used an array of bytes one to one with the size of the layout of the class. However, we have some test cases for outrageously large explicit layout structures and classes which cause this approach to OOM in crossgen2.

The fix is to move to a data structure defined in terms of intervals. This is probably a bit slower, but it requires vastly less memory for pathological situations.

Fixes #55164
Fixes #53559