[FEATURE] Add stdWrap for _DEFAULT_PI_VARS

This feature allows multilevel variables as well.

Example:
plugin.tt_news._DEFAULT_PI_VARS {
  year.stdWrap.data = date:Y
}

Change-Id: I49ae6b420f98cf959f95289c99c49d7636a4ba52
Resolves: #22045
Releases: 6.2
Reviewed-on: https://review.typo3.org/14283
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe