Fixing setting focus when RCTView is not yet in window

[nakambo]

Please select one of the following

• I am removing an existing difference between facebook/react-native and microsoft/react-native-macos 👍
• I am cherry-picking a change from Facebook's react-native into microsoft/react-native-macos 👍
• I am making a fix / change for the macOS implementation of react-native
• I am making a change required for Microsoft usage of react-native

Summary

I have a scenario where I send the focus command to a component from it's componentDidMount lifecycle, which leads native code to try to set focus to a RCTView with a zero frame (okay...) that isn't in a window (also seems unexpected). Not surprisingly, not being in a window means the view can't be focused. For comparison, I have the same behavior working as expected on the Win32\Office flavor of React Native.

I see there's existing code that tries to deal with this for a particular RCTBaseTextInputView, but nothing generically for RCTView. I'm trying to extend that to the RCTView. As part of that, I considered using the existing pending focus flag, but that seems suspect because we could have multiple views competing for focus -- so I am opting to change it to a single, weak ref for the currently pending focus view (which we clear if someone else grabs, or attempts to grab focus, or if the pending view later resigns focus, in addition to the scenario already handled viz. pending focus view gets focus).

Changelog

[macOS/iOS] [Changed] - Extend reactFocusIfNeeded to work with any generic RCTView

Test Plan

I have been able to validate these changes against 0.66 for my scenario.
I have added a test page to RNTester to check before\after (repro before, resolved after)

[Saadnajmi]

Two questions:

1. This feels like something we could upstream to RN Core, now that iOS/iPadOS is more window aware. Maybe we can see what we can do to drive that..

2. Supposing we can't upstream to RN Core, any objection to keeping the reactFocusIfNeeded naming? My reason for that is I'd like to minimize diffs if possible. It looks like RN Core implemented that logic specifically for since that's probably the only iOS control they actually care about focus for

EDIT: I see now you kept reactFocusIfNeeded, and reactViewDidMoveToWindow is on top of that. So better questions:

1. Can we upstream the "pendingFocusView" stuff
2. If not, we'll need to add more //TODO(macOS) tags to mark the diff.

[nakambo]

Two questions:

1. This feels like something we could upstream to RN Core, now that iOS/iPadOS is more window aware. Maybe we can see what we can do to drive that..
2. Supposing we can't upstream to RN Core, any objection to keeping the reactFocusIfNeeded naming? My reason for that is I'd like to minimize diffs if possible. It looks like RN Core implemented that logic specifically for since that's probably the only iOS control they actually care about focus for

EDIT: I see now you kept reactFocusIfNeeded, and reactViewDidMoveToWindow is on top of that. So better questions:

1. Can we upstream the "pendingFocusView" stuff
2. If not, we'll need to add more //TODO(macOS) tags to mark the diff.

How about I add the tags for now?

I need this to mitigate a11y concerns for my feature, which can't proceed without these fixes, which is also why for expediency I am making (proposing) these changes to the Microsoft fork.

[Saadnajmi]

Wanna double check the diffs with Core, but tested and works fine! Textinput autofocus isn't broken on iOS or macOS, and the new FocusOnMount page works on macOS :)