src/vs/workbench/common/editor/editorGroupModel.ts/EditorGroupModel/isPinned
class EditorGroupModel:	isPinned(editorOrIndex: EditorInput | number): boolean {
		let editor: EditorInput;
		if (typeof editorOrIndex === 'number') {
			editor = this.editors[editorOrIndex];
		} else {
			editor = editorOrIndex;
		}

		return !this.matches(this.preview, editor);
	}