src/vs/workbench/contrib/tasks/browser/terminalTaskSystem.ts/VariableResolver/replacer
class VariableResolver:	private async replacer(match: string, args: string[]): Promise<string> {
		// Strip out the ${} because the map contains them variables without those characters.
		let result = this.values.get(match.substring(2, match.length - 1));
		if ((result !== undefined) && (result !== null)) {
			return result;
		}
		if (this._service) {
			return this._service.resolveAsync(this.workspaceFolder, match);
		}
		return match;
	}