Added misc query tests for $regex

[vic-tsang]

This PR contains:

• query tests for $regex

Ref:

• Issue Add compatibility test for query: element and evaluation operators (7 total) #33

[documentdb-triage-tool]

🤖 Auto-triaged by documentdb-triage-tool.

Applied: compatibility test, enhancement
Project fields suggested: Component test-coverage · Priority P2 · Effort XL · Status Needs Review
Confidence: 0.85 (mixed)

Reasoning

component from path globs (test-coverage, test-framework); effort from diff stats (1998+4 LOC, 9 files); LLM: Adds new query test coverage for the $regex operator, expanding compatibility test suite as tracked by Issue #33.

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