SDL3 backend text input does not work about imgui

[ocornut]

This is possibly fixed by #7452 . I’ll try to get to it early next week.

[ocornut]

I have pushed said fix, however, note that IME inputs are currently essentially broken because somehow the keys (e.g. arrows, enter) gets sent to both the IME and the app, and app reacting to it usually means unfocusing the text widget.

I'm not sure how to fix that, I would appreciate if someone with SDL3 interest could investigate it.

I'm puzzled by SDL3 messing with system IME, when things would just work by default if didn't mess with it.

I'm also puzzled by the SDL_StartTextInput() design. Currently in other backends it is always possible for apps/widgets to access characters. It's not possible with SDL3. I think there are situation where OSD keyboard may be opt-in rather than always on. e.g. if you want to implement a Windows Explorer-style "typing select" feature you need to read characters without an always-visible prompt.