[regexp] Use required literal filter to speed up matching

[Hans-Halverson]

Summary

Use the RequiredLiteralFilter introduced in #501 during matching. This filter allows us to 1) filter out any inputs that never contain the required literal and 2) if the literal has a known bound from the start of the match, restricts match start positions that need to be checked. Is used in combination with the MatchStartFilter in order to further optimize where the backtracking matcher even needs to be run.

Notes:

• Required literal search is specialized for the "matches can only appear at the start" case by restricting search to bounded window, if possible.
• We must conservatively widen the search window in HeapTwoByteCodePointLexerStream to account for code points that take two code units.

Seeing a massive +62.6% increase to Octane RegExp benchmark score from this change, an a +3.3% overall improvement to Octane score.

Tests

• Added LLM-generated integration tests exercising the required literal filter in a variety of situations