[Chapel Merge] Improve spec for out intent

Branch: refs/heads/master
Revision: 4ec7c20
Author: mppf
Log Message:

Merge pull request #17242 from mppf/improve-spec-out-intent

Improve spec for out intent

This PR updates the spec to describe changes in out and `inout
intents as a follow-up to PRs #16990 and #17231.

Reviewed by @vasslitvinov - thanks!

Modified Files:
M doc/rst/language/spec/procedures.rst

Compare: https://github.com/chapel-lang/chapel/compare/ba03bb073c9e...4ec7c20ab323