Mark null and undefined as undetectable, and use it to handle abstract equality comparison in the generic compare ic

Marking as undetectable makes abstract equality of null, undefined, and
other undetectable objects easier. Supporting it in the generic compare
IC significantly speeds up dynamic comparison between those values and
JSReceivers by not falling back to the runtime.

MIPS port contributed by Balazs Kilvady <balazs.kilvady@imgtec.com>

Review URL: https://codereview.chromium.org/1683643002

Cr-Commit-Position: refs/heads/master@{#33858}