Add getAuth() default arg to all entry points

[hsubox76]

getAuth() is implemented separately in each auth entry point file. #4702 added a default app param value in only the browser index.ts entry point. Adding to the other entry points for consistency.

Fixes #4949

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Latest commit: c6fd598

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[google-oss-bot]

Binary Size Report

Affected SDKs

No changes between base commit (d9dc89f) and head commit (24ff1a39).

Test Logs

• Base (d9dc89ff): https://github.com/firebase/firebase-js-sdk/actions/runs/965489823
• Head (24ff1a39): https://github.com/firebase/firebase-js-sdk/actions/runs/965867387

[google-oss-bot]

Size Analysis Report

Affected Products

No changes between base commit (d9dc89f) and head commit (24ff1a39).

Test Logs

• Base (d9dc89f): https://github.com/firebase/firebase-js-sdk/actions/runs/965489823
• Head (24ff1a39): https://github.com/firebase/firebase-js-sdk/actions/runs/965867387