Expand deprecation policy to package:flutter_driver

[Piinks]

This is the tracking issue for the proposal to expand the deprecation policy to package:flutter_driver

Now that flutter and flutter_test have been successfully adopted, we are looking to expand the deprecation policy to other packages, with flutter_driver being next.

This will involve:

• adding dart fix support to flutter_driver
• advance communication to users and a feedback period
• deprecation notice formatting enforcement
• updating the deprecation policy on the wiki and website to list enforced packages

If we were to do this after the next release (not the current round in #139243 but the next round), these would be up for removal:

class / method	property	deprecated in
CommandHandlerFactory	_waitUntilNoTransientCallbacks	1.9
CommandHandlerFactory	_waitUntilNoPendingFrame	1.9
CommandHandlerFactory	_waitUntilFirstFrameRasterized	1.9
FlutterDriver	enableAccessibility	2.3
TimelineSummary	writeSummaryToFile	2.1

[ImadBouirmane]

Thanks @Piinks
It's really helpful 👌🏻