render xterm instead of html for the chat terminal output

[meganrogge]

fixes #276946

[Copilot]

Pull Request Overview

This PR refactors terminal command output rendering to use xterm's VT sequences instead of HTML serialization. The change introduces a new DetachedTerminalCommandMirror class that creates a detached terminal instance to render command output using VT sequences, replacing the previous HTML-based approach.

Key changes:

• Introduces DetachedTerminalCommandMirror class to handle VT-based terminal rendering
• Adds getRangeAsVT() method to XtermTerminal for extracting VT sequences between markers
• Removes fallback output parameter and HTML serialization logic from TerminalCommandArtifactCollector
• Simplifies ChatTerminalToolOutputSection by removing HTML sanitization and static output rendering

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
chatTerminalCommandMirror.ts	New class that creates detached terminal instances to render command output using VT sequences
xtermTerminal.ts	Adds getRangeAsVT() method to extract VT sequences between markers using the serialize addon
terminal.ts	Adds getRangeAsVT() interface method and makes raw property available on IDetachedXtermTerminal
terminalCommandArtifactCollector.ts	Simplifies capture logic by removing HTML serialization and fallback output handling
runInTerminalTool.ts	Updates calls to remove fallback output parameter
chatTerminalToolProgressPart.ts	Major refactor to use VT rendering instead of HTML, removes sanitization logic
chatTerminalToolProgressPart.css	Updates styles for terminal container and adds styling for empty state

addressed

[Tyriar]

We want some unit tests for this, they'll be a lot more important in the next PR though. Basically they should write stuff to XtermTerminal, pass in the command and verify they both serialize to the same text. For the streaming PR we want it to check as things are progressing.

addressed