Pull out ACL scheduling into a separate class

There are no logical changes in this CL, it just splits out logic from
acl_manager into a reusable class.

Test: all existing tests
Bug: 246640776
Tag: #refactor
BYPASS_LONG_LINES_REASON: Bluetooth

Change-Id: I66902d20e013e83e1127dacae418b83917ea7a4c