Added projection test cases for positional $

[vic-tsang]

This PR contains:

• projection test cases for positional $

Ref:

• Issue Add compatibility test for projection operators (3 total) #29

[documentdb-triage-tool]

🤖 Auto-triaged by documentdb-triage-tool.

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

Reasoning

component from path globs (test-coverage, test-framework); effort from diff stats (1378+0 LOC, 9 files); LLM: Adds new test cases for positional $ projection operator, expanding compatibility test coverage.

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