Raise/Drop objection Automatically with UVM

Variable uvm_sequence_base::starting_phase is deprecated and replaced by two new methods set_starting_phase and get_starting_phase, which prevent starting_phase from being modified in the middle of a phase. This change is not backward-compatible with UVM 1.1, though variable starting_phase, although deprecated, has not yet been removed from the base class library. New method uvm_sequence_base::set_automatic_phase_objection causes raise_objection and drop_objection…