feat(firestore): Add array expressions

[milaGGL]

Add new array expressions arrayFirst, arrayFirstN, arrayLast, arrayLastN, arrayMinimumN,arrayMaximumN, arrayIndexOf, arrayLastIndexOf, arrayIndexOfAll.

ported from firebase/firebase-js-sdk#9492

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[dlarocque]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a comprehensive set of new array expressions to the Firestore Pipeline API, including arrayFirst, arrayFirstN, arrayLast, arrayLastN, arrayMinimumN, arrayMaximumN, arrayIndexOf, arrayLastIndexOf, and arrayIndexOfAll. The changes are well-implemented across the API, implementation, and documentation files. The accompanying integration tests are thorough, covering both basic usage and various edge cases, which ensures the reliability of these new features.

The code quality is high, and the new additions are consistent with the existing API design. I have only a couple of minor suggestions to improve code style in the tests by using let instead of var for variables that are not reassigned.

Overall, this is an excellent contribution that significantly enhances the array manipulation capabilities of Firestore pipelines.