Mark signal APIs as unstable (denoland#3779)

cli/js/lib.deno_runtime.d.ts

@@ -2130,8 +2130,11 @@ declare namespace Deno {
  */
  export const args: string[];
 
- /** SignalStream represents the stream of signals, implements both
- * AsyncIterator and PromiseLike */
+ /** UNSTABLE new API.
+ *
+ * SignalStream represents the stream of signals, implements both
+ * AsyncIterator and PromiseLike
+ */
  export class SignalStream implements AsyncIterator<void>, PromiseLike<void> {
  constructor(signal: typeof Deno.Signal);
  then<T, S>(
@@ -2142,7 +2145,9 @@ declare namespace Deno {
  [Symbol.asyncIterator](): AsyncIterator<void>;
  dispose(): void;
  }
- /**
+
+ /** UNSTABLE new API.
+ *
  * Returns the stream of the given signal number. You can use it as an async
  * iterator.
  *
@@ -2168,6 +2173,8 @@ declare namespace Deno {
  * The above for-await loop exits after 5 seconds when sig.dispose() is called.
  */
  export function signal(signo: number): SignalStream;
+
+ /** UNSTABLE new API. */
  export const signals: {
  /** Returns the stream of SIGALRM signals.
  * This method is the shorthand for Deno.signal(Deno.Signal.SIGALRM). */