libterm: bring across changes from term

libterm: bring across changes from term

This brings across changes made to the term library to libterm. This
includes removing instances or unwrap, fixing format string handling, and
removing a TODO.

This fix does not bring all changes across, as term now relies on cargo
deps that cannot be brought into the rust build at this stage, but has
attempted as best to cross port changes not relying on this. This notably
limits extra functionality since implemented int he Terminal trait in
Term.

This is in partly in response to rust issue #29992.