unicode (proof of concept)

[koal44]

branch: https://github.com/koal44/xterm.js/tree/poc/unicode-hell

run the demo, enable the compat-addon in the width tab, and try your usual unicode test cases in bash/zsh/fish/pwsh. it renders modern unicode grapheme clusters over a legacy wcwidth-style model while remaining in sync with the backend app and supporting atomic cursor movement and deletion.