sync xterm's textarea with buffer contents

[meganrogge]

fixes #186904

[meganrogge]

@Tyriar mostly working now, except if I do cmd+backspace. When I put a breakpoint here, it works 🤔. This also does not work when I blur (focus out) the terminal. Tried handling focus change and syncing when that happens and didn't work

textarea.mov

vscode/src/vs/workbench/contrib/terminal/browser/xterm/xtermTerminal.ts

Line 283 in 84f8417

const textArea = this.raw.textarea;

[meganrogge]

surprising errors given I didn't change this line 🤔

vscode/src/vs/platform/terminal/common/capabilities/commandDetectionCapability.ts

Lines 14 to 16 in e151ba5

	// Importing types is safe in any layer
	// eslint-disable-next-line local/code-import-patterns
	import type { IBuffer, IBufferLine, IDisposable, IMarker, Terminal } from 'xterm-headless';

[Tyriar]

Looks good after the couple of comments

Not sure about the monaco check failure, @hediet do you know why it thinks platform/terminal is part of monaco?