[flang] Improve runtime crash messages

Where possible, I added additional information to the messages to help
programmers figure out what went wrong.  I also removed all uses of the word
"bad" from the messages since (to me) that implies a moral judgement rather
than a programming error.  I replaced it with either "invalid" or "unsupported"
where appropriate.

Differential Revision: https://reviews.llvm.org/D121493