Handle Keyboard input on Android

[DrSloth]

Description

Hello there, i am currently trying to implement an android app using egui and winit. As it seems Keyboard Input is currently not supported on Android. I already got the keyboard to open up using jni in my app.

However the "text" field of the KeyEvents seems to be empty and non ascii chars don't seem to be supported.

I am already investigating this and would absolutely love some pointers to implementing this and hopefully getting this into a release version of winit to support egui on android.

Relevant platforms

Android

[kchibisov]

See #2993

If you feel like making to work on it, comment on this PR.