src/vs/workbench/api/common/extHostDiagnostics.ts/DiagnosticCollection/clear
class DiagnosticCollection:	clear(): void {
		this._checkDisposed();
		this._onDidChangeDiagnostics.fire([...this._data.keys()]);
		this._data.clear();
		if (this._proxy) {
			this._proxy.$clear(this._owner);
		}
	}