Support ILink.dispose

When displaying hovers/overlays using the link provider API currently
it's not possible to know when unused links are no longer cached in
xterm.js which can result in leaked event listeners.

src/browser/Linkifier2.ts

@@ -125,6 +125,13 @@ export class Linkifier2 extends Disposable implements ILinkifier2 {
 
   private _askForLink(position: IBufferCellPosition, useLineCache: boolean): void {
     if (!this._activeProviderReplies || !useLineCache) {
+      this._activeProviderReplies?.forEach(reply => {
+        reply?.forEach(linkWithState => {
+          if (linkWithState.link.dispose) {
+            linkWithState.link.dispose();
+          }
+        });
+      });
       this._activeProviderReplies = new Map();
       this._activeLine = position.y;
     }

src/browser/Types.d.ts

@@ -275,6 +275,7 @@ interface ILink {
   activate(event: MouseEvent, text: string): void;
   hover?(event: MouseEvent, text: string): void;
   leave?(event: MouseEvent, text: string): void;
+  dispose?(): void;
 }
 
 interface ILinkDecorations {