Streamline rent/return on ArrayPool (#55710)

* Streamline rent/return on ArrayPool

- Stop storing and using a _bucketArraySizes.  It's cheaper to recompute the shift on each use than it is to index into the array (with a bounds check).  Plus less memory.
- The 99% case is renting a positive length for pooled array sizes (especially now that we've bumped the limit up to a gig).  Move the checks for lengths <= 0 to after the check for whether the length is poolable.
- Move arrays into locals to enable the JIT to eliminate some bounds checks.
- Use ThrowHelpers where we already have them
- Move non-generic helpers out of generic class into Utilities
- Consolidate buffer allocation in Rent to a single line
- Reorganize TLS checks to be as early as possible
- Use FastMod instead of % in per-core stacks

* Address PR feedback