[TASK] Clean up typolink target and linktxt

Rename $linktxt to $linkText.
Only evaluate target if forceTarget is not set.

Add a small helper method to call parseFunc on empty
$linkText that is used in 4 places within typoLink().

Resolves: #74318
Releases: master
Change-Id: I043ba3192be83ec6acf28cb88a287be1b8cd74fa
Reviewed-on: https://review.typo3.org/47095


Reviewed-by: Mathias Schreiber <mathias.schreiber@wmdb.de>
Tested-by: Mathias Schreiber <mathias.schreiber@wmdb.de>
Reviewed-by: Eugen Lang <laeu1011+gerrit@gmail.com>
Tested-by: Eugen Lang <laeu1011+gerrit@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>