Add api to propagating translation capability updates.

This change adda the apia in the TranslationService that allows to
update the TranslationCapability to the registered clients. This
change doesn't contain the register part in the TranslationManager,
the change will be done on the next change.

Bug: 176208267
Test: atest CtsTranslationTestCases
Test: manual verification
CTS-Coverage-Bug: 182990474

Change-Id: Iec7b3dc30f99985415162394d0e64d8e825ea5d9