feature: Add option supportedModes

[defuncart]

📜 Description

Adds the option to define supportedModes so that, for instance, FeedbackMode.navigate is not displayed.

💡 Motivation and Context

For a single page desktop application, the navigate option may not be required. Moreover, the user can continue to interact with the application as usual (i.e. right click), thus there can be cases where we do not want to allow the user to interact while the feedback window is open.

Conversely, I am not sure if there are real-world use-cases where the user can interact/navigate but not draw, nevertheless those would be covered by this PR.

💚 How did you test it?

Update example/lib/main.dart, change supportedModes accordingly.

Technically the user can select

mode: FeedbackMode.draw,
supportedModes: const [FeedbackMode.navigate],

which is non-sensical. A check in FeedbackWidget ensures correct state, however the api could be updated, i.e. first value of supportedModes.

Moreover, assets/errors could be raised when supportedModes is empty;

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• I updated the docs if needed
• All tests passing
• No breaking changes

🔮 Next steps

• FeedbackMode.navigate perhaps needs a renaming to interactive. This, perhaps, could be more descriptive. Such a change, however, would be a breaking change best suited to another PR.
• mode was left as-is to not introduce any breaking changes (see discussion above).

[defuncart]

@ueman Thanks for creating this package :) Please review API and let me know what you think. Once API is approved, appropriate tests can be added.

[ueman]

Hey, thanks for the contribution. The API seems perfectly fine for me. Thanks for working on it.

[codecov]

Codecov Report

Attention: Patch coverage is 96.29630% with 1 line in your changes missing coverage. Please review.

Project coverage is 83.77%. Comparing base (471cc7b) to head (df234c7).
Report is 15 commits behind head on master.

Files with missing lines	Patch %	Lines
feedback/lib/src/feedback_widget.dart	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #276      +/-   ##
==========================================
- Coverage   83.77%   83.77%   -0.01%     
==========================================
  Files          20       20              
  Lines         635      641       +6     
==========================================
+ Hits          532      537       +5     
- Misses        103      104       +1     

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