Firestore: Factor out logic that extracts paths from package.json in rollup scripts

[dconeybe]

This PR adds the function getPackageJsonExportPaths() to rollup.shared.js so that the rollup scripts can access the "exports" paths from package.json in a consistent way, rather than the random bespoke ways. This should help to improve the readability of the rollup scripts.

Work In Progress

This PR is a work-in-progress. As of Jan 22, 2024, work on this PR has been de-prioritized but I'm leaving it here so it can be picked up in the future. Googlers see b/302682954 for details.

[changeset-bot]

⚠️ No Changeset found

Latest commit: bddda9d

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[google-oss-bot]

Size Report ¹

Affected Products

No changes between base commit (991fa27) and merge commit (52f3a0b).

Test Logs

• Base (991fa27): https://github.com/firebase/firebase-js-sdk/actions/runs/7537086987
• Merge (52f3a0b): https://github.com/firebase/firebase-js-sdk/actions/runs/7546669044

1. https://storage.googleapis.com/firebase-sdk-metric-reports/C0Buv0XGDN.html

[google-oss-bot]

Size Analysis Report ¹

Affected Products

No changes between base commit (991fa27) and merge commit (52f3a0b).

Test Logs

• Base (991fa27): https://github.com/firebase/firebase-js-sdk/actions/runs/7537086987
• Merge (52f3a0b): https://github.com/firebase/firebase-js-sdk/actions/runs/7546669044

1. https://storage.googleapis.com/firebase-sdk-metric-reports/yRPCITUyes.html