Deflake registerLinkProvider tests

The root cause of this flakiness problem was related to the click event
handler. For some reason it would not go off on some links but it would
when clicking elsewhere in the terminal. I tried a bunch of things to
keep the click handler to no avail, instead opting to move to using
mousedown and mouseup events for activating links which comes with the
nice benefit of ensuring that the link on mouseup is the same one on
mousedown.

Fixes #3821

src/browser/Linkifier2.ts

@@ -18,6 +18,7 @@ export class Linkifier2 extends Disposable implements ILinkifier2 {
   private _linkProviders: ILinkProvider[] = [];
   public get currentLink(): ILinkWithState | undefined { return this._currentLink; }
   protected _currentLink: ILinkWithState | undefined;
+  private _mouseDownLink: ILinkWithState | undefined;
   private _lastMouseEvent: MouseEvent | undefined;
   private _linkCacheDisposables: IDisposable[] = [];
   private _lastBufferCell: IBufferCellPosition | undefined;
@@ -61,7 +62,8 @@ export class Linkifier2 extends Disposable implements ILinkifier2 {
       this._clearCurrentLink();
     }));
     this.register(addDisposableDomListener(this._element, 'mousemove', this._onMouseMove.bind(this)));
-    this.register(addDisposableDomListener(this._element, 'click', this._onClick.bind(this)));
+    this.register(addDisposableDomListener(this._element, 'mousedown', this._handleMouseDown.bind(this)));
+    this.register(addDisposableDomListener(this._element, 'mouseup', this._handleMouseUp.bind(this)));
   }
 
   private _onMouseMove(event: MouseEvent): void {
@@ -129,7 +131,7 @@ export class Linkifier2 extends Disposable implements ILinkifier2 {
     let linkProvided = false;
 
     // There is no link cached, so ask for one
-    this._linkProviders.forEach((linkProvider, i) => {
+    for (const [i, linkProvider] of this._linkProviders.entries()) {
       if (useLineCache) {
         const existingReply = this._activeProviderReplies?.get(i);
         // If there isn't a reply, the provider hasn't responded yet.
@@ -156,7 +158,7 @@ export class Linkifier2 extends Disposable implements ILinkifier2 {
           }
         });
       }
-    });
+    }
   }
 
   private _removeIntersectingLinks(y: number, replies: Map<Number, ILinkWithState[] | undefined>): void {
@@ -222,18 +224,21 @@ export class Linkifier2 extends Disposable implements ILinkifier2 {
     return linkProvided;
   }
 
-  private _onClick(event: MouseEvent): void {
+  private _handleMouseDown(): void {
+    this._mouseDownLink = this._currentLink;
+  }
+
+  private _handleMouseUp(event: MouseEvent): void {
     if (!this._element || !this._mouseService || !this._currentLink) {
       return;
     }
 
     const position = this._positionFromMouseEvent(event, this._element, this._mouseService);
-
     if (!position) {
       return;
     }
 
-    if (this._linkAtPosition(this._currentLink.link, position)) {
+    if (this._mouseDownLink === this._currentLink && this._linkAtPosition(this._currentLink.link, position)) {
       this._currentLink.link.activate(event, this._currentLink.link.text);
     }
   }