[flang] Add a derived type component visitor framework

After fixing 594, it appears there were issues in
FindUltimateComponent that was considering type bound
procedure as components.
This commit fixes and beef-up the component visitation by making a visitor
class for it. The main advantage of making it an class vs functions is that
it is possible to get the component chain to the result component for better
feedback for the user.
The framework allow a single place to define/handle what ultimate, direct and
potential components are.

Original-commit: flang-compiler/f18@d84821a1d63f35904a004007f3645d689d8c3a4f
Reviewed-on: https://github.com/flang-compiler/f18/pull/607
Tree-same-pre-rewrite: false