Feat: Hide sensitive content in screenshot

[JakesMD]

📜 Description

I added the ability to hide sensitive content in draw mode and in the screenshot itself.

Changes:

• Created a FeedbackRedacted widget that blurs its child in draw mode and in the screenshot.
• Created a FeedbackRedactionController to notify FeedbackRedacted widgets of changes to the redaction state.
• Added a redaction controller to FeedbackController.
• Added a redactionController.unredact() call to FeedbackController.hide().
• Added the logic to FeedbackWidget to redact and unredact depending on the mode and whether a screenshot is being taken.
• Updated README.md

💡 Motivation and Context

Helps devs comply with privacy regulations.

The option to detect for SensitiveContent widgets was explored, but it's practically impossible to accurately find out whether a SensitiveContent widget is visible or even just partially obscured (see #378 (comment)).

Fixes #378

💚 How did you test it?

• Wrapped the counter text in the test app with a FeedbackRedacted widget
• Updated existing widget tests to also check for blurring depending on mode an so on.
• Added a test to FeedbackController to check that unredact() is called during hide()
• Added FeedbackRedactionController tests to check that it's notifying listeners.

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• I updated the docs if needed
• All tests passing except the ones that were already failing
• No breaking changes