[Chapel Merge] Restore CHPL_REGEXP to ChapelEnv module, but mark

Branch: refs/heads/main
Revision: 40f98d4
Author: lydia-duncan
Log Message:

Merge pull request #18004 from lydia-duncan/deprecateRegexp

Restore CHPL_REGEXP to ChapelEnv module, but mark it as deprecated
[reviewed by @bradcray]

Also:

  • don't add it to the documentation
  • set it to CHPL_RE2 instead of restoring the compiler variable it used to
    correspond to
  • don't use split initialization because that triggered the deprecation warning

Add a deprecation test to lock in the deprecation message - note that this
uses a different environment variable than the other regex tests in that
directory

Passed a full paratest with futures and CHPL_RE2 = bundled. Double checked
that the skipif fired appropriately when CHPL_RE2 = none

Modified Files:
A test/deprecated/ChapelEnv-CHPL_REGEXP.chpl

A test/deprecated/ChapelEnv-CHPL_REGEXP.good
A test/deprecated/ChapelEnv-CHPL_REGEXP.skipif
M modules/standard/ChapelEnv.chpl

Compare: https://github.com/chapel-lang/chapel/compare/7d128e8f32d6...40f98d45a388