src/vs/workbench/api/common/extHostDiagnostics.ts/ExtHostDiagnostics/_mapper
class ExtHostDiagnostics:	static _mapper(last: vscode.Uri[]): { uris: readonly vscode.Uri[] } {
		const map = new ResourceMap<vscode.Uri>();
		for (const uri of last) {
			map.set(uri, uri);
		}
		return { uris: Object.freeze(Array.from(map.values())) };
	}