Held Write Acks Changelog entries
As per
+# Unreleased
+- [changed] Changed the internal handling for locally updated documents that
+ haven't yet been read back from Cloud Firestore. This can lead to slight
+ behavior changes and may affect the `SnapshotMetadata.hasPendingWrites()`
+ metadata flag.
+- [changed] Eliminated superfluous update events for locally cached documents
+ that are known to lag behind the server version. Instead, we buffer these
+ events until the client has caught up with the server.
+
# 17.1.1
- [fixed] Fixed an issue where the first `get()` call made after being offline
could incorrectly return cached data without attempting to reach the backend.
