Internationalize subclasses of NumberKeyListener

The previous implementation assumed ASCII digits, and a fixed set of
separators and signs.

The following classes have been internationalized: DigitsKeyListener,
DateKeyListener, TimeKeyListener, and DateTimeKeyListener.
DialerKeyListener is not modified yet, due to concerns about the
handling of non-ASCII digits by dialing-related parts of Android.

Even with this CL, characters outside BMP and multi-character signs
and decimal separators are still not supported, due to limitations in
android.view.KeyEvent and android.view.KeyCharacterMap.

Test: cts-tradefed run cts-dev --module CtsTextTestCases --test android.text.method.cts.*KeyListenerTest
Bug: https://code.google.com/p/android/issues/detail?id=2626
Bug: https://code.google.com/p/android/issues/detail?id=82993
Bug: 8319249
Bug: 33276673
Bug: 33643035
Bug: 34394455
Change-Id: I1cf87d0d9d1b383f5265c07ecd63b5767f9a68ca