Add deprecation warning on Signal blocking feature (#521)

* Add deprecation warning on `[I]Signal.block`
Make `ISignal.block` optional

* Add deprecation warning on `Signal.blockAll`

Author: fcollonval

packages/signaling/src/index.ts

@@ -38,9 +38,11 @@ export interface ISignal<T, U> {
    * ### Notes
    * The callback function must be synchronous.
    *
+   * @deprecated This feature will be removed in Lumino 2.
+   *
    * @param fn The callback during which the signal is blocked
    */
-  block(fn: () => void): void;
+  block?(fn: () => void): void;
 
   /**
    * Connect a slot to the signal.
@@ -154,6 +156,8 @@ export class Signal<T, U> implements ISignal<T, U> {
    * ### Notes
    * The callback function must be synchronous.
    *
+   * @deprecated This feature will be removed in Lumino 2.
+   *
    * @param fn The callback during which the signal is blocked
    */
   block(fn: () => void): void {
@@ -223,6 +227,8 @@ export namespace Signal {
    * ### Notes
    * The callback function must be synchronous.
    *
+   * @deprecated This feature will be removed in Lumino 2.
+   *
    * @param sender The signals sender
    * @param fn The callback during which all signals are blocked
    */