LSP extensionFactory is never called for file editors

[krassowski]

Description

JupyterLab 4.1 introduced extensionFactory (#14920) to enable adapter-aware code editor extensions; it works fine for notebooks but not at all in file editors. This is because it is instantiated by EditorAdapter which is created when an editor (e.g. cell) gets added to a widget adapter:

jupyterlab/packages/lsp/src/adapters/adapter.ts

Lines 620 to 631 in 2d68127

	private _onEditorAdded(
	sender: WidgetLSPAdapter<T>,
	change: IEditorChangedData
	): void {
	const { editor } = change;
	const editorAdapter = new EditorAdapter({
	editor: editor,
	widgetAdapter: this,
	extensions: this.options.featureManager.extensionFactories()
	});
	this._editorToAdapter.set(editor, editorAdapter);
	}

While notebook adapter correctly emits this signal when new cells get added:

jupyterlab/packages/notebook/src/notebooklspadapter.ts

Lines 468 to 470 in 2d68127

	this._editorAdded.emit({
	editor
	});

It is never emitted from file adapter

jupyterlab/packages/fileeditor/src/fileeditorlspadapter.ts

Line 25 in 2d68127

export class FileEditorAdapter extends WidgetLSPAdapter<

Expected behavior

Editor extensions registered on LSP manager using widgetFactory in file editor too.

Context

• JupyterLab version: 4.1.2