Merge branch 'bc/fix-update-data' of github.com:firebase/firebase-js-sdk into bc/fix-update-data

Author: Brian Chen

.changeset/clean-cameras-check.md

@@ -2,4 +2,4 @@
 '@firebase/firestore': minor
 ---
 
-Fixed a bug where `UpdateData` did not recognize optional, dot-separated string fields.
+Fixed a bug where `UpdateData` did not recognize union types or optional, dot-separated string fields.