Android: Support unicode character mapping + dead keys

[rib]

Up until now the Android backend has been directly mapping key codes which essentially just represent the "physical" cap of the key (quoted since this also related to virtual keyboards).

Since we didn't account for any meta keys either it meant the backend only supported a 1:1 mapping from key codes, which only covers a tiny subset of characters. For example you couldn't type a colon since there's no keycode for that and we didn't try and map Shift+Semicolon into a colon character.

This has been tricky to support because the NativeActivity class doesn't have direct access to the Java KeyEvent object which exposes a more convenient getUnicodeChar API.

It is now possible to query a KeyCharcterMap for the device associated with a KeyEvent via the AndroidApp::device_key_character_map API which provides a binding to the SDK KeyCharacterMap API in Java:

https://developer.android.com/reference/android/view/KeyCharacterMap

This is effectively what getUnicodeChar is implemented based on and is a bit more general purpose.

KeyCharacterMap lets us map a key_code + meta_state from a KeyEvent into either a unicode character or dead key accent that can be combined with the following key. This mapping is done based on the user's chosen layout for the keyboard.

To enable support for key character maps the
AndroidApp::input_events() API was replaced by
AndroidApp::input_events_iter() which returns a (lending) iterator for events. This was changed because the previous design made it difficult to allow other AndroidApp APIs to be used while iterating events (mainly because AndroidApp held a lock over the backend during iteration)

• Tested on all platforms changed
• Added an entry to CHANGELOG.md if knowledge of this change could be valuable to users
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• Created or updated an example program if it would help users understand this functionality
• Updated feature matrix, if new features were added or implemented

--

Note: this currently depends on a git branch of android-activity https://github.com/rust-mobile/android-activity/tree/rib/pr/input-api-rework-with-key-character-maps which I'm aiming to land soon in preparation for a 0.5 release of android-activity in time for Winit 0.29

[kchibisov]

Should be good after you fix formatting.

[rib]

For reference here, I've landed the corresponding support in android-activity main (after also reverting back to a rust-version of 1.64) so the updated Cargo.toml now pulls android-activity from main.

I could potentially do a 0.5 beta release if needs be, to avoid the temporary git dependency.

One small tweak that was made before I merged the android-activity API was to rename get_dead_key to get_dead_char since that's what the corresponding Android SDK is called.