[Chapel Merge] Add a warning to the I/O style section of the IO d

Branch: refs/heads/main
Revision: a1c787a
Author: lydia-duncan
Link: https://github.com/chapel-lang/chapel/pull/19228
Log Message:

Merge pull request #19228 from lydia-duncan/removeIOStyleDoc

Add a warning to the I/O style section of the IO docs and remove a note
[reviewed by @mppf]

The iostyle record is now deprecated, so the documentation about using it
needed to reflect that. There was a note in that section about it being a work
in progress - remove that note, since we don't intend to improve iostyle
itself any more.

Double-checked the built docs look good with this change

Modified Files:
M modules/standard/IO.chpl

Compare: https://github.com/chapel-lang/chapel/compare/adb82427f6b7...a1c787a8f934