Prevent concurrent modifiation of Call mExtras.

The entrypoints to Call#putExtras and Call#removeExtras are not all threadsafe which was resulting in Concurrent Modification Exceptions being thrown. To resolve this, this CL ensures all points of entry to these methods are synchronized upstream on Telecom's mLock.

Bug: 261946446
Test: Manual Test
Change-Id: If3e0291df9a3fc93a844b0289468e051411fd676