Add video priority to Process.java

The definitions in Process.java need to be kept in sync with
definitions in system/core/libsystem/include/system/thread_defs.h.
This CL adds the video thread priority to Process.java
because it was previously added only to thread_defs.h.

bug:65462846
test: make, make offline-sdk-docs
Change-Id: I5fdbcc91adbb11179ab57c9e9e257411aac33686