Fix setting `onFocus` callback for `SemanticsAction.focus` on iOS. about flutter HOT 2 CLOSED

Tried on flutter/engine@205a241 (which didn't work), documenting how I did that:

Build the iOS simulator and host engine with the fix (my machine is arm64):

$ gh pr checkout 53285
$ et build -c ios_debug_sim_arm64 && et build -c host_debug_unopt_arm64

In the framework cherry-pick #142942:

$ git cherry-pick dd700e6

Set up the test to run against the local engine with the fix (see #149741 (comment) for more details):

$ cd dev/integration_tests/ios_platform_view_tests
$ flutter build ios --config-only --local-engine ios_debug_sim_arm64 --local-engine-host host_debug_unopt_arm64
$ open ios/Runner.xcworkspace

In Xcode open PlatformViewUITests and run testPlatformViewFocus.

from flutter.

Closing in favor of #150030.

from flutter.