[TASK] Deprecate single slash comments in TypoScript

Double slash one-line comments are standard in many languages.
Make them standard in TypoScript, too.

Deprecated:
  / Line comment headed by single slash

Resolves: #76104
Releases: master
Change-Id: Id78391f973cdf8147bf91b269996f31d475de717
Reviewed-on: https://review.typo3.org/48051


Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>