Add telecom log marking shell command.

We often get bugs where testers have executed a LONG list of test steps.
It becomes extremely difficult to know where in the logs corresponds to
which test script step.

This adds a new telecom shell command:
adb shell telecom log-mark Testing 1 2 3

This command adds a USER_LOG_MARK event log item to all ongoing calls and
to the general telecom logs with the specified message.

Test: Tested using the new shell command to mark the telecom logs in and out of calls.
Fixes: 228895073
Change-Id: Ic11edc777e57a4fc8748a42c931379faf7cea671