Rearchitect DumpManager to be registry-only

This CL attempts to rework DumpManager to be a registry-only class,
where DumpsysEntrys can be registered to participate in the system
dumpsys, but the overall collection can be inspected by commands such as
DumpHandler and LogBufferCommand

Test: DumpManagerTest
Test: DumpHandlerTest
Bug: 278094048
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:3737b7e34d74d1c13e1f6f6012d06372d3389caa)
Merged-In: Ic71e03fe54a7e07caaf8679a93d0e7e56606162a

Change-Id: Ic71e03fe54a7e07caaf8679a93d0e7e56606162a