Rename and reset the proirity of HID host thread

* Rename the HH event polling thread to bt_hh_thread
* HH event polling thread is created by bt_main_thread
  with RT priority. Lower the thread priority since the
  tasks in this thread is not timing critical

Bug: 131787936
Test: Connect to a HID device
      Run "adb shell ps -A -T -Z -O rtprio"
Change-Id: Ibd983e96bc339393842d4c2e2aa226534095e225
Merged-In: Ibd983e96bc339393842d4c2e2aa226534095e225