Implement new replacedBy dart fix for current and prior deprecations

[Piinks]

The dart fix has a new feature, replacedBy. This allows us to make transformations across classes.
The feature resolved dart-lang/sdk#45393, which has some example use cases.

We should implement this for current deprecations, and check to see if any past deprecations that have already been removed can be supplied a fix.

⭐ It has not been confirmed that we can provide fixes for these, but they should each be investigated. Some may still be too complex to reliably migrate, or may not provide a better experience to the developer if it can only partially be fixed.

Might be able to fix, will check them off as they are investigated:

	Old API	New API
✅	DayPicker	CalendarDatePicker
✅	MonthPicker	CalendarDatePicker
✅	FlatButton	TextButton
✅	OutlineButton	OutlinedButton
✅	RaisedButton	ElevatedButton
	Scaffold.[snackbars]	ScaffoldMessenger.[snackbars]
	BlacklistingTextInputFormatter	FilteringTextInputFormatter
	WhitelistingTextInputFormatter	FilteringTextInputFormatter
	CupertinoNavigationBar.actionsForegroundColor	CupertinoTheme.primaryColor
	CupertinoSliverNavigationBar.actionsForegroundColor	CupertinoTheme.primaryColor
	ButtonTheme.bar	ButtonBarTheme

These are just the ones I thought of or saw might be possible from the ones we have announced. If anyone can think of others, let us know and we'll add them to the list!

[Piinks]

Related dart fix feature requests:

• Insert a comment through a dart fix dart-lang/sdk#47945
• Allow skip on dart fix rules dart-lang/sdk#47944
• Allow expression in code template to be conditional dart-lang/sdk#47943
• fix_data.yaml compiled from multiple files dart-lang/sdk#47941

[Piinks]

The button and Month/Date picker migrations were not possible with replacedBy, they were still too complex to create a transformation of code that would actually be helpful to the user.
I feel the SnackBar one is similar, since many folks save a reference, use a key, or chain off of .of(context) to use that API. I don't think dart fix can reliably catch these, but it is still worth checking.

The remaining ones to explore are listed above. I am not currently working on this, so I am going to un-assign myself.

@TahaTesser has been exploring fixes, do not feel obligated to work on this. Just an FYI in case you are interested as part of your fix library. :)