[editor] chinese input method error

[502647092]

Description

at theia when I input at input method then backspace it some thing at editor will clear

I test at monaco don't have this bug

Reproduction Steps

see gif
OS and Theia version:
Diagnostics:

[monaka]

I got the almost same issue on Che-Theia with ChromeOS/Japanese input method.

I suspect the root cause is "Current Theia doesn't care about KeyCode.KEY_IN_COMPOSITION."
This will be not the issue of Monaco but Theia.
I found the similar issue report in VSCode and there looks be fixed by microsoft/vscode#40546.

I guess there needs some more code in packages/core/src/browser/widgets/widget.ts or near.

[monaka]

gitpod-io/gitpod#875 also will be fixed if this issue was fixed.