Merge changes I7950b5b8,If6fdb8a4,I5fa84727,I3d926464

* changes:
  simpleperf: warn branch count overflow in inject cmd.
  simpleperf: support merging branch_list files in inject cmd.
  simpleperf: merge branch lists before converting them to autofdo.
  simpleperf: split code doing different conversions in InjectCommand.