[TASK] Code cleanup for RteHtmlParser

Several code parts have been cleaned up and sorted into separate methods
to ensure readability.

Certain options defined by procOptions are now initialized at the very
beginning, before all transformations.

Resolving modes are moved into a separate method, as well as configuring
the entry- and exit-HTML parser, making the main method easier to read.

Cleaning up content and adding <p> tags around "simple" content lines
has been split up as well to avoid code duplication.

Resolves: #79280
Releases: master
Change-Id: Ib734a8cedebff3cc0b415155b6328bf3a77841e9
Reviewed-on: https://review.typo3.org/51268


Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>