13212 Add trace events around custom compositor callbacks. (cla: yes)

13213 Re-land “Custom compositor layers must take into account the device pixel ratio.” (cla: yes)

13214 Forwards Activity result to FlutterFragment in FlutterFragmentActivity. (cla: yes)

13215 Adds Dark Mode support to new Android embedding (this was accidentally missed previously). (cla: yes)

13216 Reland icu upgrade (cla: yes)

13218 Specify a human readable reason for an error from the embedder API. (cla: yes)

13232 Avoid dereferencing IO manager weak pointers on the UI thread (CQ+1, cla: yes)

13233 Update ui.instantiateImageCodec docs to reflect what it does. (cla: yes)