google_cloud_firestore

Why this change is needed:
Prepares non-breaking patch releases for google_cloud_firestore and
firebase_admin_sdk by dropping WIP staging suffixes and updating version
constants after landing stability fixes and custom headers support.

Summary of changes:

• Bump google_cloud_firestore version to 0.5.3 in pubspec and changelog.
• Remove -wip suffix from firebase_admin_sdk to stage release 0.5.4.
• Add recent Storage.delete() idempotency bugfix item to changelog.
• Regenerate version.g.dart constant to match 0.5.4.

• Added Settings.headers to attach custom HTTP headers to every outgoing Firestore request.
• Fixed intermittent ClientException: Connection closed before full header was received on queries and aggregations under high concurrency; these now retry with backoff.
• Fixed Firestore.getAll() retrying transient errors indefinitely; it now retries a bounded number of times before surfacing the error.
• Updated Transaction.delete and Transaction.update type constraints to accept DocumentReference<Object?>. (thanks to @Levin-Me)
• Made Timestamp encodable by adding toJson method. (thanks to @OutdatedGuy)
• Update dependency googleapis_auth: ^2.3.3 to fix auth/insufficient-permission errors with Application Default Credentials that have no quota project set.

• Fixed Firestore.projectId not reading GOOGLE_CLOUD_PROJECT when using Application Default Credentials locally.
• Fixed FieldMask not available from export. (thanks to @OutdatedGuy)
• Require google_cloud: '>=0.4.0 <0.6.0'

• Added retry support for WriteBatch.commit() on transient errors (ABORTED, UNAVAILABLE, RESOURCE_EXHAUSTED).
• Added an example.
• Added a more detailed project description.
• Update dependency meta: ^1.17.0 to allow workspaces with stable Flutter.

• First release.