src/vs/workbench/common/editor/editorGroupModel.ts/EditorGroupModel/doUnstick
class EditorGroupModel:	private doUnstick(editor: EditorInput, index: number): void {
		if (!this.isSticky(index)) {
			return; // can only unstick a sticky editor
		}

		// Move editor to be the first non-sticky editor
		this.moveEditor(editor, this.sticky);

		// Adjust sticky index
		this.sticky--;

		// Event
		this._onDidChangeEditorSticky.fire(editor);
	}