Integrated editor in webview

[sguillia]

Summary
Allow to create our own "Interactive Playgrounds" mixing HTML and integrated editors.

Description
VS Code has a nice interactive playground, which is a webview with integrated editors.

Help > Interactive Playground

There editors embed all the features of a default text editor:

• syntax highlighting
• autocompletion
• extension contributions
• ...

I would like to create a webview containing editors like that.

Currently, we can only create webviews with an HTML textarea, like this.

The content of the Interactive Playground is here

vscode/src/vs/workbench/contrib/welcome/walkThrough/browser/editor/vs_code_editor_walkthrough.ts

Lines 132 to 143 in 72c700c

	### Errors and Warnings
	Errors and warnings are highlighted as you edit your code with squiggles. In the sample below you can see a number of syntax errors. By pressing kb(editor.action.marker.nextInFiles) you can navigate across them in sequence and see the detailed error message. As you correct them the squiggles and scrollbar indicators will update.
	|||js
	// This code has a few syntax errors
	Console.log(add(1, 1.5));
	function Add(a : Number, b : Number) : Int {
	return a + b;
	}
	|||

Relates to #77131 even if this can apply to webviews that are not custom editors

[vscodebot]

(Experimental duplicate detection)
Thanks for submitting this issue. Please also check if it is already covered by an existing one, like:

• "Extract to..." in Interactive Playground fails (#75137)

[mjbvz]

Duplicate of #93265