src/vs/platform/extensionManagement/node/extensionManagementService.ts/ExtensionManagementService/filterUninstalled
class ExtensionManagementService:	private async filterUninstalled(...identifiers: ExtensionIdentifierWithVersion[]): Promise<string[]> {
		const uninstalled: string[] = [];
		const allUninstalled = await this.extensionsScanner.getUninstalledExtensions();
		for (const identifier of identifiers) {
			if (!!allUninstalled[identifier.key()]) {
				uninstalled.push(identifier.key());
			}
		}
		return uninstalled;
	}