[flang] Fix location of name of Symbol for ProcEntity

When we encounter a ProcDecl and a symbol for it has already been
created, replace the CharBlock for the name with the one in the ProcDecl
as it is the "main" declaration of that name. This matches what is done
for an EntityDecl.

This moves the location of some error messages to a better source
location so update the affected tests.

Original-commit: flang-compiler/f18@514c0f2c9477040f830fbf0495e4d38129648615
Reviewed-on: https://github.com/flang-compiler/f18/pull/1080
Tree-same-pre-rewrite: false