Instead of a function taking an enum value determining which path to
return, we now have a suite of functions, each returning a single path
kind. This makes it easy to move the python-path function into a
specific plugin in a follow-up commit.
All the users of GetLLDBPath were converted to call specific functions
instead. Most of them were hard-coding the enum value anyway, so this
conversion was simple. The only exception was SBHostOS, which I've
changed to use a switch on the incoming enum value.