fix(ios): iOS 13.4 subkey menu workaround

[jahorton]

A temporary workaround for #2716.

Unfortunately, Apple broke something in iOS 13.4 that we've been heavily relying upon for longpresses on the keyboard. Longpresses that start within a WKWebView can now be blocked by JS events, which completely broke all subkey menus.

This PR will adapt Keyman for iOS to rely on Web-side longpress detection instead. Unfortunately, web-side longpresses can't exactly control Swift-side UI, but we can at least trigger display of the subkey menus.

With this workaround in place, once the subkey menu displays, the user must start a second touch within that menu in order to select whatever key/option they desire. We simply can't tie the menu-generating longpress to the Swift UI, unfortunately. So, it won't be as smooth as before, but at least it'll work on iOS 13.4, which is (hopefully) an acceptable tradeoff. We'll want a more robust solution in the long-term, but far more work than this will be required to make that happen.

Currently addressed:

• Popup keys now usable
• Globe-based keyboard menu now usable

[mcdurdin]

I don't think that's going to be a workable solution, sorry :(

[jahorton]

Hmm... it'll definitely still need some work. Interestingly, while it can display popup keys out of the base keyboard bounds in-app, touches don't seem to work... but only when started outside of those bounds. (You can tap inside the bounds and then move the touch, at which point it will follow.)

Also, there's the matter of undoing a popup-key menu display; we'd also (ideally) add a 'cancel' operation.

[mcdurdin]

Test notes - mostly reflecting what you've already written. Testing on iOS 12.4.

1. Long press is now visible again and can be selected. Requires a release and new gesture to select an item.
2. Long press can only be cancelled by releasing and pressing on the active base key. Particularly tricky for a two-level long press menu on the top row, where there are only a handful of pixels that you can touch to cancel, because the menu is shifted down over the base key in order to fit in bounds!
3. Long press outside keyboard bounds on in-app keyboard popup has no effect; as you found, you must drag from within the keyboard bounds, starting somewhere on the long press menu itself, in order to select these long press keys. Tricky!

Assuming we can resolve points 2 & 3 above, can we disable the workaround for iOS < 13.4 so that users on older versions aren't adversely affected by this?

[mcdurdin]

LGTM.

Let's keep monitoring the iOS 13.4.x situation along with your bug report and see if it gets resolved and we can roll back in the future.

Is it possible to link Apple's bug report id in somewhere? I know it's private to you but we can still refer to it in communications with Apple in the future.

[jahorton]

I'm not finding a way to link it yet, but here's the raw data that we could use with them:

Apr 3, 2020 at 1:44 PM – FB7650067