fix: memory leak in abstract task service

[SimonSiefke]

Fixes a memory leak in ProblemReporter and AbstractTaskService.

Details

The Emitter in ProblemReporter currently doesn't seem be registered as a Disposable:

class ProblemReporter implements TaskConfig.IProblemReporter {

	private _validationStatus: ValidationStatus;
	private readonly _onDidError: Emitter<string> = new Emitter<string>(); // not registered
	public readonly onDidError: Event<string> = this._onDidError.event;

Therefore one change is registering the Emitter as a Disposable.

---

Another issue seems to be when calling AbstractTaskService._computeWorkspaceFolderTasks multiple times and using this._register:

private async _computeWorkspaceFolderTasks(workspaceFolder: IWorkspaceFolder, runSource: TaskRunSource = TaskRunSource.User): Promise<IWorkspaceFolderTaskResult> {
	/* ... */
	const problemReporter = new ProblemReporter(this._outputChannel);
	this._register(problemReporter.onDidError(error => this._showOutput(runSource, undefined, error)));

Since there is only one AbstractTaskService, registering a disposable each time when calling _computeWorkspaceFolderTasks seems make the number of registered disposables grow each time.

By changing it to a DisposableMap the DisposableMap ensures that there is only one problemsReporter disposableStore per workspaceUri. And calling this._workspaceTaskDisposables.set(workspaceFolder.uri, store) automatically disposes the previous registered disposableStore for that workspace uri.

private async _computeWorkspaceFolderTasks(workspaceFolder: IWorkspaceFolder, runSource: TaskRunSource = TaskRunSource.User): Promise<IWorkspaceFolderTaskResult> {
	/* ... */
	const store = new DisposableStore();
	this._workspaceTaskDisposables.set(workspaceFolder.uri, store);
	const problemReporter = store.add(new ProblemReporter(this._outputChannel));
	store.add(problemReporter.onDidError(error => this._showOutput(runSource, undefined, error)));

Before

When configuring a task 37 times, the number of various functions in AbstractTaskService._computeWorkspaceFolderTasks and some other places seems to grow each time:

After

When configuring a task 37 times, while the number of some functions still grows, for AbstractTaskService._computeWorkspaceFolderTasks it stays constant now:

[meganrogge]

Thank you!