[BUGFIX] PAGE_TSCONFIG_ID in flex form fields

PAGE_TSCONFIG_ID, PAGE_TSCONFIG_IDLIST and PAGE_TSCONFIG_STR to
replace markers in foreign_table_where fields could only be set
for flex forms on a global level in the past:

TCEFORM.tt_content.pi_flexform.PAGE_TSCONFIG_ID = 42

This has the negative side effect that also fields from
potentially foreign plugins could have been affected by that.
With the FormEngine rewrite, this change only worked if restricted
to specific elements of a specific data structure:

TCEFORM.tt_content.pi_flexform.news.sDEF.settings\.categories.PAGE_TSCONFIG_ID = 42

The former "global" setting was broken and is fixed by the
patch with a hack. For master, this very hack is deprecated
now and only the specific version is allowed, for 7.6 both versions
work with the patch.

Note there is no setting for those foreign_table_where clauses
for section container elements anymore that is not deprecated.

Change-Id: I3f7bede86007f7ea1703f2bc569e0152e67802e6
Resolves: #73209
Releases: master, 7.6
Reviewed-on: https://review.typo3.org/47924


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>