Refactor the TraceurMessenger code into a ServiceConnection class.

This change has identical behavior to the code that was already there.
The reason behind it is to distinguish the behavioral changes from the
refactor for the following code changes to the Issue Recording Service
code.

Bug: 364824477
Test: Verified that this code still works the exact same as before.
Flag: EXEMPT non-behavioral, small refactor
Change-Id: I3d320d84392393cf27e05a6a9202872c0f2b6a7d