src/vs/editor/contrib/snippet/browser/snippetVariables.ts/CompositeSnippetVariableResolver/resolve
class CompositeSnippetVariableResolver:	resolve(variable: Variable): string | undefined {
		for (const delegate of this._delegates) {
			const value = delegate.resolve(variable);
			if (value !== undefined) {
				return value;
			}
		}
		return undefined;
	}