[Enhancement] Use TaskCreationOptions.RunContinuationsAsynchronously when creating a TaskCompletionSource

From [this guide](https://github.com/davidfowl/AspNetCoreDiagnosticScenarios/blob/master/AsyncGuidance.md#always-create-taskcompletionsourcet-with-taskcreationoptionsruncontinuationsasynchronously) would be good if all `TaskCompletionSource` used in MAUI have the `TaskCreationOptions.RunContinuationsAsynchronously` in his constructor, this will avoid dead-locks.

```csharp

// Instead of doing this
var tcs = new TaskCompletionSource();

// do this
var tcs = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
```

From the guide:
> Always use TaskCreationOptions.RunContinuationsAsynchronously when creating the TaskCompletionSource. This will dispatch the continuation onto the thread pool instead of executing it inline.

Since .NET MAUI is a UI framework this will need some investigation to see if there's any problem with that, in other words, risk of trying to change some UI control in `non-MainThread`.

Search the MAUI repository for every TaskCompletionSource construction and identify the affected platform-specific and shared code paths. Review the linked AsyncGuidance guidance and verify that applying the option does not cause UI updates from a non-main thread; done means the relevant usages are updated and the existing tests pass.

Written by the indexing model from the issue text.