FIX: sort strings in UTF-8 encoded byte order

[milaGGL]

Strings should be sorted in UTF-8 encoded byte order. Public document: https://cloud.google.com/firestore/docs/concepts/data-types#data_types

SDK sorts strings using built in comparator method, which sorts lexicographically, and leads to mismatch between server and sdk when special characters are present. This PR fixes the string order mismatches on document field, map key, and document key.

[github-actions]

Release note changes

The following release notes were modified. Please ensure they look correct.

Release Notes

firebase-firestore

### {{firestore}} version 25.1.2 {: #firestore_v25-1-2}

* {{fixed}} Fixed a server and sdk mismatch in unicode string sorting. GitHub [#6615](//github.com/firebase/firebase-android-sdk/issues/6615){: .external}

#### {{firestore}} Kotlin extensions version 25.1.2 {: #firestore-ktx_v25-1-2}

The Kotlin extensions library transitively includes the updated
`firebase-firestore` library. The Kotlin extensions library has no additional
updates.

[github-actions]

Vertex AI Mock Responses Check ⚠️

A newer major version of the mock responses for Vertex AI unit tests is available. update_responses.sh should be updated to clone the latest version of the responses: v5.3

[github-actions]

Test Results

  186 files  +  144    186 suites  +144   4m 19s ⏱️ + 2m 57s
1 234 tests +  912  1 218 ✅ +  896  16 💤 +16  0 ❌ ±0 
2 492 runs  +1 836  2 460 ✅ +1 804  32 💤 +32  0 ❌ ±0 

Results for commit 4987548. ± Comparison against base commit b5dbd0a.

This pull request removes 322 and adds 1234 tests. Note that renamed tests count towards both.

com.google.firebase.remoteconfig.ConfigTests ‑ Custom Signals builder support multiple types
com.google.firebase.remoteconfig.ConfigTests ‑ Firebase#remoteConfig should delegate to FirebaseRemoteConfig#getInstance()
com.google.firebase.remoteconfig.ConfigTests ‑ Firebase#remoteConfig should delegate to FirebaseRemoteConfig#getInstance(FirebaseApp, region)
com.google.firebase.remoteconfig.ConfigTests ‑ FirebaseRemoteConfigSettings builder works
com.google.firebase.remoteconfig.ConfigTests ‑ Overloaded get() operator returns default value when key doesn't exist
com.google.firebase.remoteconfig.ConfigTests ‑ Overloaded get() operator returns value when key exists
com.google.firebase.remoteconfig.CustomSignalsTest ‑ testCustomSignals_builderPutDouble
com.google.firebase.remoteconfig.CustomSignalsTest ‑ testCustomSignals_builderPutDuplicateKeys
com.google.firebase.remoteconfig.CustomSignalsTest ‑ testCustomSignals_builderPutLong
com.google.firebase.remoteconfig.CustomSignalsTest ‑ testCustomSignals_builderPutMixedTypes
…

com.google.firebase.firestore.AggregateQuerySnapshotTest ‑ createWithCountShouldReturnInstanceWithTheGivenQueryAndCount
com.google.firebase.firestore.AggregateQueryTest ‑ testSourceMustNotBeNull
com.google.firebase.firestore.BlobTest ‑ testComparison
com.google.firebase.firestore.BlobTest ‑ testEquals
com.google.firebase.firestore.BlobTest ‑ testMutableBytes
com.google.firebase.firestore.CollectionReferenceTest ‑ testEquals
com.google.firebase.firestore.DocumentChangeTest ‑ randomTests
com.google.firebase.firestore.DocumentChangeTest ‑ testAdditions
com.google.firebase.firestore.DocumentChangeTest ‑ testChangesWithSortOrderChange
com.google.firebase.firestore.DocumentChangeTest ‑ testDeletions
…

♻️ This comment has been updated with latest results.

[google-oss-bot]

Coverage Report ¹

Affected Products

• firebase-firestore

  Overall coverage changed from 45.74% (b5dbd0a) to 45.73% (242064a) by -0.01%.

  Filename	Base (b5dbd0a)	Merge (242064a)	Diff
  LruGarbageCollector.java	97.27%	93.64%	-3.64%
  PatchMutation.java	100.00%	98.39%	-1.61%
  SetMutation.java	94.44%	97.22%	+2.78%
  Util.java	73.38%	73.94%	+0.56%

Test Logs

• Base (b5dbd0a): https://github.com/firebase/firebase-android-sdk/actions/runs/12663446756
• Merge (242064a): https://github.com/firebase/firebase-android-sdk/actions/runs/12793003513

1. https://storage.googleapis.com/firebase-sdk-metric-reports/sfp8M5CeVW.html

[google-oss-bot]

Size Report ¹

Affected Products

• firebase-firestore

  Type	Base (b5dbd0a)	Merge (242064a)	Diff
  aar	1.45 MB	1.45 MB	+133 B (+0.0%)
  apk (release)	11.4 MB	11.4 MB	+64 B (+0.0%)

Test Logs

• Base (b5dbd0a): https://github.com/firebase/firebase-android-sdk/actions/runs/12663446756
• Merge (242064a): https://github.com/firebase/firebase-android-sdk/actions/runs/12793003513

1. https://storage.googleapis.com/firebase-sdk-metric-reports/3X9VBHr9lQ.html