NBLog: refactor Writer API for extensibility

No new functionality was added, and no existing functionality was
removed.

Event types have been renamed and reorganized according to
functionality. A compile-time mapping from Event to C++ data type allows
for a generic Event log() template function to avoid the need to add a
new logging function when a new Event is added to enum NBLog::Event.

Most LockedWriter functions were deleted because they did not involve
accessing shared variables. Only the functions that accessed shared
variables were kept in LockedWriter.

Test: dumpsys media.log -r
Bug: 68148948
Change-Id: I8a27f1690795cdb0b84e92033b7cbf4588ba175e