Improve error messages from Patrol methods

[jBorkowska]

Here will be listed issues with Patrol error messages.

• when scrollTo() hasn't found any widget that matches provided finder within a timeout:
  

• When first/last/at() is called on a finder that doesn't find any widgets:

  $(Button).first, findsNothing); // "StateError (Bad state: no element)" instead of passing expect()

[bartekpacia]

I'd prefer to create separate issues for specific errors, and have a milestone called e.g. "Better logging". But feel free to comment anyway, we'll can do that afterward.

See also:

• patrol test should display logs using flutter logs #860

[jBorkowska]

Separate issues will be created later.

[bartekpacia]

This PR is about improving error messages from Custom Finders-related functionality only. I'm afraid there's not much we can do without sacrificing the safety checks we currently get by using functions from TestAsyncUtils class from flutter_test.

More context: There's an open Flutter issue about this problem, which is essentially a bug the core Dart package called stack_trace.

In Patrol, there are also issues/PRs that are about improving error messages from Native Automation-related functionality. See:

• Fix error reports containing "Multiple errors were thrown" without any helpful information #981
• Test reports don't contain useful info ("Multiple exceptions were thrown") #951

[bartekpacia]

See also:

• WidgetTester.dragUntilVisible() to show helpful errors flutter/flutter#89336

[jBorkowska]

First problem will be fixed with scrolling rework (see #1325), second one is not very important right now

[bartekpacia]

Possibly related: dart-lang/sdk#46318