extensions/references-view/src/tree.ts/SymbolsTree/clearInput
class SymbolsTree:	clearInput(): void {
		this._sessionDisposable?.dispose();
		this._input = undefined;
		this._ctxHasResult.set(false);
		this._ctxInputSource.reset();
		this._tree.title = localize('title', 'References');
		this._tree.message = this._history.size === 0
			? localize('noresult', 'No results.')
			: localize('noresult2', 'No results. Try running a previous search again:');
		this._provider.update(Promise.resolve(this._history));
	}