[flang] Improve error reporting for procedures determined by usage (#88184)
When a symbol is known to be a procedure due to its being referenced as
a function or subroutine, improve the error messages that appear if the
symbol is also used as an object by attaching the source location of its
procedural use. Also, for errors spotted in name resolution due to how a
given symbol has been used, don't unconditionally set the symbol's error
flag (which is otherwise generally a good idea, to prevent cascades of
errors), so that more unrelated errors related to usage will appear.