Added geospatial tests for $center

[vic-tsang]

This PR contains:

• geospatial tests for $center

Ref:

• Issue Add compatibility test for query: geospatial operators (11 total) #32

[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); effort from diff stats (1110+0 LOC, 8 files); LLM: Adds new geospatial test coverage for the $center operator, expanding compatibility test suite under the test-coverage component.

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