Introduce DumpManager

Introduces DumpManager, a unified dumping system that supports dumping
at different priority levels.

Currently, when a bug report gets taken, SystemUI is only dumped during
the CRITICAL section. This has its advantages (we get to go first!) but
also imposes a strict limit on how much we can dump. To get around this
restriction, we need to *also* dump SystemUI during the NORMAL section,
which has much more forgiving constraints.

This CL simply creates the mechanism for systemUI to dump at different
priority levels, but doesn't actually cause us to participate in the
NORMAL section (yet, see later CLs).

It introduces the DumpManager, unified replacement for DumpController &
various logic in SystemUIService and Dependency.java. See kdoc in
DumpManager for usage notes.

Migration of current users of DumpController coming in a later CL.

Test: atest, manual
Change-Id: If4f41ed496c0c64024a83aad812b77f60fe27555