Add helpers for TableLogBuffer + TableLogBufferFactory for tests.

1) Adds Kosmos.tableLogBufferFactory and uses it in tests.
2) Adds a helper method to create real TableLogBuffers with just a name
   and either a Kosmos instance or a SystemClock instance.

Bug: 360832989
Flag: TEST_ONLY
Test: atest TableLogBufferFactoryTest LogDiffsForTableTest
FullMobileConnectionRepositoryTest (+ other tests)

Change-Id: I1ebd119c15b018dc74f0200369f693cff0676732