Track lock key down state instead of lock state

[gspencergoog]

Description

This converts the GTK keyboard code to track the key down states of the lock modifiers NumLock and CapsLock so that they represent the actual "down" state of the key, rather than the lock state itself.

GTK tracks the lock state, and Flutter expects the down state.

Related Issues

• Fixes Gtk Keyboard mapping thinks Num Lock is on when it isn't. flutter#60922
• Related to TextInputType.phone keyboard doesn't delete typed text when the keyboard is switched to extra symbols on Android flutter#64761

[stuartmorgan-g]

Wouldn't it make more sense for the mock engine to allow setting up an arbitrary channel to echo, rather than passing in an arbitrary channel name here, so that the changes for testing as, as much as possible, in the test code rather than the real code?

[gspencergoog]

OK @stuartmorgan , I've added an engine constructor that will allow overriding of the channel to send requests on, and used that when setting up the mock engine. Is that what you were thinking of? I still have to pass the response callback, because that's specific to the key event plugin, and it needs to terminate the event loop.

[stuartmorgan-g]

I think this is worse than what you had, sorry. Per discussion yesterday, I forgot there's no actual mock engine at this point, only a mock renderer.

Let's go back to what you had before, and longer term we'll find a better way of doing this kind of testing. (Probably using the embedder.h layer interposing that I want to write for testing all of the desktop embeddings.)

[gspencergoog]

OK, I reverted it back to what I had before.

[gspencergoog]

@dkwingsmt PTAL, I think this is ready to go in.

[dkwingsmt]

LGTM

[stuartmorgan-g]

LGTM, although my confidence in reviewing GObject code is still low.