fix: memory leak in status bar

[SimonSiefke]

Fixes a memory leak in extension host status bar items. Generated by GitHub Copilot.

When a status bar item is added with the $setEntry method, a disposable is being added:

// mainThreadStatus.ts

$setEntry(){
 // disposable added to store, but never removed from store
  this._store.add(toDisposable(() => this.statusbarService.unsetEntry(entryId)));
}

However it doesn't seem to be removed in $disposeEntry

$disposeEntry(entryId: string) {
	this.statusbarService.unsetEntry(entryId);
}

Before

When opening and closing an image editor 97 times, which registers 3 status bar items, the number of MainThreadStatusBar.$setEntry functions grows by 291 (97*3).

After

When opening and closing an image editor 97 times, the number of MainThreadStatusBar.$setEntry functions stays constant.