Replace DispatchToOGTerminal with JavaTerminal and remove the visitor

`DispatchToOGTerminal` is replaced with `JavaTerminal` so that we no longer use the visitor implementation. `JavaTerminal` uses our type dispatch mechanism in a similar way to `Real16AoA` and `Complex16AoA`.

This allows us to erase the visitor implementation that remained, since there is nothing left using it.

Coverage:

Java: unchanged.
src/jshim: 52.9%, down from 54%, because `DispatchToOGTerminal` and `JavaTerminal` have no C++ tests, and `JavaTerminal` is slightly longer.
src/librdag: 94.3% down from 94.4%, due to the removal of the accept methods which were tested.

All others unchanged.
Nice :)