Add support for frame_type and frame_description in JRuby

This commit refactors the experimental JRuby support such that
we can return roughly the same values for 'frame_type' and
'frame_description' in JRuby that we see in MRI.

This still has some limitations due to the following bugs:

https://github.com/pry/pry/issues/1205
https://github.com/pry/pry-stack_explorer/issues/20

But should be an improvement over the previous implementation.