* phase 1

* reexport

* comments

* 12.0.0 cleanup: drop deprecated API, honour ignored navigator parameters

- Remove the members that were deprecated in the 10.x series:
  CountrySelectorNavigator.addSeparator, .showCountryCode, .appBarTheme and
  .navigate, the CountryChip typedef, PhoneFormField.textAlign and
  PhoneValidator.none (README updated accordingly).
- CountrySelectorNavigator.dialog() now honours showDialCode: the parameter was
  declared but never forwarded to the base class, so dial codes were always
  displayed.
- CountrySelectorNavigator.page() now honours searchBoxDecoration,
  searchBoxTextStyle, searchBoxIconColor and scrollPhysics, which the factory
  accepted but never forwarded to the selector either.
- CountrySelectorNavigator.draggableBottomSheet() now exposes useRootNavigator.
- Rename the selector sources that hold public classes so that they no longer
  use a leading underscore, and use relative imports for lib/src internals
  (package: imports are kept for the two public entrypoints).
- Format lib/src/validation/localized_validation_error.dart and check the
  formatting of lib/test/example in CI.
- Reword the 12.0.0 changelog: there was no dependency cycle, only a one way
  dependency on flutter_country_selector and the lockstep releases it required.
- Add regression tests for the removed API and for the parameter forwarding.

* internal refactor

* upgrade versions

* tighten deps

* fix tests

* fix deprecation