[TASK] RTE Parser - store allowed tag list in class property

Instead of having a local variable list, the code is cleaned
up by moving the allowed tags list into the class property.

No change in functionality is made.

Resolves: #72852
Releases: master
Change-Id: I58e26f02a58e5feb2096caa44c6a8538d59ea9b3
Reviewed-on: https://review.typo3.org/46121


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>