[flang] Fix a crash when creating generics from a copy

Summary:
When a program unit creates a generic based on one defined in a module, the
function `CopyFrom()` is called to create the `GenericDetails`.  This function
copied the `specificProcs_` but failed to copy the `bindingNames_`.  If the
function `CheckGeneric()` then gets called, it tries to index into the empty
binding names and causes the crash.

I fixed this by adding code to `CopyFrom()` to copy the binding names.

I also added a test that causes the crash.

Reviewers: klausler, tskeith, DavidTruby

Subscribers: llvm-commits

Tags: #llvm, #flang

Differential Revision: https://reviews.llvm.org/D83491