Rename "priority" to "bias".

With the incoming priority API for apps to use, keeping the legacy
"priority" naming will increase confusion inside the codebase. Use bias
as the new name of the legacy system since it biases which jobs to run
first without being strict.

Bug: 140852299
Bug: 142272435
Test: atest frameworks/base/services/tests/mockingservicestests/src/com/android/server/job
Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/content
Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/job
Test: atest CtsJobSchedulerTestCases
Test: atest CtsSyncManagerTest#testExpeditedJobSync
Test: atest CtsSyncManagerTest#testExpeditedJobSync_InDoze
Change-Id: I338125a66484b0bb33469103ac70d2772e70395d