Call Sequencing initial changes/refactor

This CL refactors the existing transactional logic to be retrofitted to
a more general case that handles regular connection services as well.
This CL mainly just renames existing classes and moves classes around to
different directories for better clarity.

This also inserts the boilerplate code for implementing the call
sequencing related changes. Those classes are as follows:
CallSequencingController, CallsManagerSequencingAdapter,
TransactionalCallSequencingAdapter.

A separate CL will be put up that will be focused around the
actual implementation.

Bug: 327038818
Flag: com.android.server.telecom.flags.enable_call_sequencing
Test: m Telecom
Change-Id: I75bd7954f9c84affcfeff29e0f36fa09e0c56607