[CLEANUP] $LANG->JScharCode() => quoteJSvalue()

Replace JscharCode() with GeneralUtility::quoteJSvalue()

Instead of making JavaScript use a String.fromCharCode, it will now use
a sanitized quoted string.

Change-Id: Idf81d5524d4bbb60b515670aa13648aa52064905
Resolves: #55009
Releases: 6.2
Reviewed-on: https://review.typo3.org/27380
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Michiel Roos
Tested-by: Michiel Roos
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind