[Fast Pair] Add UI constants

In HalfSheet package
1. Clean up: use a prefix string to replace common package name
2. Add a ACTION_FAST_PAIR for subsequent pairing

e2e video: https://photos.app.goo.gl/WawkcRm9eND3HfBb7

Test: -m
Bug: 247152236
Ignore-AOSP-First: nearby_not_in_aosp_yet
Change-Id: I9cbe885b12d804ee3612375766d5995335f55702
1 file changed