Add IME (Input Method Editor) support

[adamjs]

Expose the input method editor API so we can support Asian text input.

[p0358]

One might find this rather useful in the meantime: https://github.com/p0358/ultralight_ime

[p0358]

It's worth noting that for AppCore apps (non-fullscreen), Windows will use fallback IME support for now, which will show preview of the prompt in the top-left corner of the screen, confirming of which will insert the full final text into the in-app's actual text prompt. The workaround I linked above is appropriate for full-screen apps (such as games).