Add 'lo-prio' tag to temp blocklist.

This is a temporary measure to allow these APIs to be identified by
downstream tooling. Before S is finished, these APIs will be moved
to the max-target-R list anyway.

Adding the lo-prio flag should have no semantic impact on these APIs
but does allow them to be distinguished from the regular blocklist
APIs.

Test: m
Bug: 174455522
Change-Id: I031dcecbdef34a4f93a0fec1a92d95f769918486