fix: memory leak in codeCell

[SimonSiefke]

fixes #186361

When scrolling a notebook up and down, I found the largest amount of detached dom nodes was this:

{
  "detachedDomNodesWithStackTraces": {
    "after": [
      {
        "className": "HTMLDivElement",
        "description": "div.monaco-editor.no-user-select.showUnused.showDeprecated.vs-dark",
        "stackTrace": [
          "View (vscode/out/vs/editor/browser/view.js:86:73)",
          "CodeEditorWidget._createView (vscode/out/vs/editor/browser/widget/codeEditorWidget.js:1483:26)",
          "CodeEditorWidget._attachModel (vscode/out/vs/editor/browser/widget/codeEditorWidget.js:1380:46)",
          "CodeEditorWidget.setModel (vscode/out/vs/editor/browser/widget/codeEditorWidget.js:415:18)",
          "vscode/out/vs/workbench/contrib/notebook/browser/view/cellParts/codeCell.js:184:46"
        ],
        "count": 3997
      }
    ]
  }
}

More details

// codeCell.ts
private initializeEditor(initEditorHeight: number) {
	const cts = new CancellationTokenSource();
	this._register({ dispose() { cts.dispose(true); } });
	raceCancellation(this.viewCell.resolveTextModel(), cts.token).then(model => {
		if (this._isDisposed) {
			return;
		}

In the initializeEditor after resolveTextModel.then the model disposable is not registered, which seemingly causes a memory leak when scrolling in the notebook.

Fix

Now the model is registered, similar to other disposables:

this._register(model);

For some reason, registering the model didn't fix the issue entirely, which is why there is also (copied from commentsController) this code:

this.templateData.editor = null!; 

With both changes in place, the number of detached div.monaco-editor dom nodes when scrolling a notebook up and down 1997 times was reduced from 3997 to 0.

[roblourens]

This seems legit, but I'll leave it to someone else to make the call

[rebornix]

@roblourens I'm not sure if it's a good idea to dispose the model since BaseCellViewModel has a model ref _textModelRef. Disposing the model here would leave us an obsolete _textModelRef and textModel.