Firestore: use string values for TargetPurpose enum

[dconeybe]

Firestore: Use string values for TargetPurpose enum, rather than numeric.

Although string values can assist with debugging, the main purpose is so that the spec tests will generate JSON for the Android and iOS SDKs that is stable and readable.

A previous PR, #7229, added TargetPurpose.ExistenceFilterMismatchBloom which caused TargetPurpose.LimboResolution to change its value from 2 to 3. This did not cause any problems in this SDK; however, it broke the spec tests in the Android SDK (and probably the ios sdk too). By hardcoding the values as strings it is both more readable and more stable.

Android port: firebase/firebase-android-sdk#4931
iOS port: firebase/firebase-ios-sdk#11191

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Latest commit: 5e43cd8

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[google-oss-bot]

Size Report ¹

Affected Products

• @firebase/firestore

  Type	Base (510c9b5)	Merge (ec2fa04)	Diff
  browser	285 kB	285 kB	+301 B (+0.1%)
  esm5	354 kB	354 kB	+301 B (+0.1%)
  main	566 kB	567 kB	+301 B (+0.1%)
  module	285 kB	285 kB	+301 B (+0.1%)
  react-native	285 kB	285 kB	+301 B (+0.1%)

• bundle

  Type	Base (510c9b5)	Merge (ec2fa04)	Diff
  firestore (Persistence)	298 kB	298 kB	+301 B (+0.1%)
  firestore (Query Cursors)	236 kB	236 kB	+281 B (+0.1%)
  firestore (Query)	234 kB	234 kB	+281 B (+0.1%)
  firestore (Read data once)	221 kB	222 kB	+281 B (+0.1%)
  firestore (Realtime updates)	223 kB	224 kB	+281 B (+0.1%)

• firebase

  Type	Base (510c9b5)	Merge (ec2fa04)	Diff
  firebase-compat.js	771 kB	772 kB	+301 B (+0.0%)
  firebase-firestore-compat.js	338 kB	338 kB	+301 B (+0.1%)
  firebase-firestore.js	344 kB	344 kB	+301 B (+0.1%)

Test Logs

• Base (510c9b5): https://github.com/firebase/firebase-js-sdk/actions/runs/4800127326
• Merge (ec2fa04): https://github.com/firebase/firebase-js-sdk/actions/runs/4800263315

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

[google-oss-bot]

Size Analysis Report ¹

This report is too large (283,134 characters) to be displayed here in a GitHub comment. Please use the below link to see the full report on Google Cloud Storage.

Test Logs

• Base (510c9b5): https://github.com/firebase/firebase-js-sdk/actions/runs/4800127326
• Merge (ec2fa04): https://github.com/firebase/firebase-js-sdk/actions/runs/4800263315

1. https://storage.googleapis.com/firebase-sdk-metric-reports/95zJtgEgRk.html

[dconeybe]

Note: The "Test Firestore" and "Test Firestore Integration" checks are failing and will be fixed by #7244.

The failing tests are:

1. Aggregation queries allows backslash in aliases when using getAggregationFromServer
2. Aggregation queries allows backticks in aliases when using getAggregationFromServer
3. Aggregation queries allows special chars in aliases when using getAggregationFromServer

Chrome Headless 112.0.5615.121 (Linux x86_64) (Persistence=false) Aggregation queries allows special chars in aliases when using getAggregationFromServer FAILED
    AssertionError: expected undefined to equal 2
Chrome Headless 112.0.5615.121 (Linux x86_64) (Persistence=false) Aggregation queries allows backticks in aliases when using getAggregationFromServer FAILED
    AssertionError: expected undefined to equal 2
Chrome Headless 112.0.5615.121 (Linux x86_64) (Persistence=false) Aggregation queries allows backslash in aliases when using getAggregationFromServer FAILED
    AssertionError: expected undefined to equal 2

[tom-andersen]

LGTM