[BUGFIX] Field pageIdSelector in RTE link popup is visible when enabled

When pageIdSelector is configured to be enabled,
a new key is added to $fieldDefinitions.
But it has no effect as long as this key is not set additionally in
$this->linkAttributes.
This patch adds this missing piece.

Resolves: #73090
Releases: master, 7.6
Change-Id: I86f83bc3292144e06c7fcc179469c715c80dcb16
Reviewed-on: https://review.typo3.org/46460


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>