feat(app): Add ability for initializeApp to accept a JSON string

[hsubox76]

This PR is built on top of #9904

(internal link) API proposal go/initializeapp-with-strings

Allows initializeApp() to be initialized with a string.

initializeApp() can currently be called with

• an object representing the Firebase config
• no arguments, if the config is available in a specific env var, a global var, or a cookie

Users often store the config as a JSON string when it needs to come from a secret or an environment variable, and then need to decode it, which can be error prone. To avoid this, users often store each property in separate secrets or environment variables, which can be cumbersome.

This change also accepts a JSON stringified string as an argument and automatically JSON.parses it, throwing an actionable error if the parse fails.

[changeset-bot]

🦋 Changeset detected

Latest commit: 5d80c59

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@firebase/app	Minor
firebase	Minor
@firebase/app-compat	Patch

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[gemini-code-assist]

Code Review

This pull request enables the initialization of FirebaseApp and FirebaseServerApp instances using JSON configuration strings, including necessary updates to the API surface, error handling for JSON parsing, and expanded test coverage. The review feedback identifies several areas for improvement, including correcting JSDoc parameter documentation, implementing safer type validation for parsed JSON objects, updating a misleading test description, and removing a duplicate test case.