Extend FeedbackThemeData to cover more widgets

[TonyD-TuftAndPaw]

Is your feature request related to a problem? Please describe.
While there are fields for bottomSheetDescriptionStyle and bottomSheetTextInputStyle, there are no equivalent ways to set the styles for the Navigate, Draw, or Submit text buttons. Similarly, there's no way to set custom icons for the undo, trash, and close buttons. And we can't change the TextInput at all (like adding a hint).

Describe the solution you'd like
I could make a case that FeedbackThemeData should have more settings to expose these things to the user. And that's the easiest way forward.

I could also make a case that widgets or widget builders should be passed in as arguments, so the developer has complete control over the widget instead of just the style. That way, for example, the "Submit" button could be split into two buttons, one to submit via email, and one to save on device. Or add max character counts to the textfield.

Describe alternatives you've considered
Nothing outside of forking the package and hardcoding our preferred styles.

Additional context
It's a great package, it's just a little too hard to customize!