[2/4] Add user customizable keys (4) for RCU in frameworks/base

Define 4 new keys, update the "last key" test case, and assign
values in Generic.kl.
Project details can be found at
go/dipper-custom-button

Bug: 269742724
Test: local build

Change-Id: If0b12be56fea1a39192da068abdacde8d3e0948f