[flang] Handle instantiation of procedure pointer components

We were not instantiating procedure pointer components.  If the instantiation
contained errors, we were not reporting them.  This resulted in internal errors
in later processing.

I fixed this by adding code in .../lib/Semantics/type.cpp in
InstantiateComponent() to handle a component with ProcEntityDetails.  I also
added several tests for various good and bad instantiations of procedure
pointer components.

Differential Revision: https://reviews.llvm.org/D100341