[DOCS] Document new TypoScript condition `tree.rootLineParentIds`

The new TypoScript condition `tree.rootLineIds` which was introduced
with #88962 is currently not documented in the original feature RST
where the new symfony expression language was introduced.

In order to keep the list of available TypoScript conditions up to date
in this document, the new condition was added accordingly.

Additionally, some minor code highlights were fixed in the document.

Related: #90221
Releases: master
Change-Id: Ib7aef851d10361b9de124cb55ba8a005d1b2d6c4
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63050


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Björn Jacob <bjoern.jacob@tritum.de>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Björn Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>