Set input thread priority to RT

To improve input latency, set the critical input threads to RT priority.
This will use RT priority on AOSP devices by default. OEMs can still
choose to customize what "input policy" means for their device, which
may not necessarily mean RT.

For example, on device with multiple small / big cores, input task
affinity could be changed to prioritize big cores + higher CPU frequency
/ voltage, but still keep the standard / default input thread priority.

With this patch, I'm finding that sometimes, one of the critical input
threads has priority 100 instead of the expected 98. Still looking into
that specific issue, but the issue is already present with the existing
"input policy" code.

Bug: 330719044
Flag: com.android.input.flags.enable_input_policy_profile
Test: took perfetto trace and checked the priority on InputDispatcher
and InputReader threads.

Change-Id: I75b6a726f0d066f16bdec26f6cf90721479d17ff