[!!!][TASK] Prepare richtext configuration

Configuring a richtext field in TCA with the "defaultExtras"
setting (which was formerly the 5th showitem parameter) has
been ugly ever since: The DataHandler needed a special _TRANSFORM_
field to trigger required RTE transformations, further config
depends on pageTs settings.

The patch gets rid of "defaultExtras" for richtext elements and
adds a new option "enableRichtext=true" within the config section
for type=text TCA fields.
This setting can be set via "columnsOverrides" for specific types, too.

As an intermediate solution, the configuration class "Richtext" is
added to fetch richtext configuration. This will be extended with
another patch to provide ckeditor configuration on TCA level.

Change-Id: I70f4cb26e2a45629b99680e532d376538afd2b90
Resolves: #79341
Releases: master
Reviewed-on: https://review.typo3.org/51311


Reviewed-by: Frans Saris <franssaris@gmail.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>