Changes on the ContentCaptureContext APIs.

- Replaced URI by a generic ID
  (which is a new class LocusId, and required)
- Createad a new Intent.ACTION_VIEW_LOCUS action
  (and Intent.EXTRA_LOCUS_ID extra)
- Removed ContentCaptureContext.getAction()
  (so the only "supported" action is ACTION_VIEW_LOCUS)
- Made the ContentCaptureContext getters public
  (getId(), getExtras())

Test: m update-api
Test: atest CtsContentCaptureServiceTestCases \
      CtsContentTestCases:LocusIdTest \
      FrameworksCoreTests:android.view.contentcapture.ContentCaptureEventTest

Bug: 123577059
Fixes: 124266664

Change-Id: Id4c28f056eb7a24dd083303ffdea7cf662cefac2