CJK IME (Sogou) input broken on Windows in Electron 13

[Eugeny]

IME bug of the day: Sogou input doesn't trigger compositionend when hosting xterm in Electron 13.

Repro: yarn electron https://xtermjs.org.

The only usable event is input with .composed && .inputType == "insertText", but that is currently being ignored due to the Linux IME fix in #3533. I'm going to try to figure out a way to distinguish between these events, but it's possible that xterm is going to need a way for the user to indicate the platform it's running on, or some sort of a "quirks mode".

It's also possible that Sogou's internal "whitelist" doesn't recognize Electron 13 (microsoft/vscode#115814 (comment))

[Eugeny]

Reference traces:

• Windows Chrome / Sogou IME

• Windows Electron 13 / Sogou IME

• Windows / emoji IME

• macOS / emoji IME

• macOS / composition

• Linux / compose key

• Linux Chrome / Sogou IME

• Linux Electron 13 / Sogou IME

Summary

Sogou

• Windows / Chrome: input/insertText -> compositionend -> keyup
• Windows / Electron 13: input/insertText -> keyup
• Linux: keydown -> input/insertText -> keyup

Emoji

• Windows: compositionend with the emoji
• macOS: input/insertText with the emoji, .composed = false

Notes

As it appears, neither keydown nor compositionend are reliable. input is the only one that's consistent across all platforms (except Windows emoji IME)