[BUGFIX] Ensure "pid" and "parentid" of pages - inline fields are correct

When doing translations with pages and inline elements (e.g. pages.media),
there is an inconsistency when an additional inline element is added to the
TRANSLATED page (e.g. language=1).

Current (wrong) when adding a translation to a page
- localized IRRE children get pid = default page ID (correct)
- localized IRRE children only localization get parentid = default page ID (should be translated page ID)

Current (wrong) behaviour when adding a IRRE child only available in a translation:
- parentid gets localized page => correct
- pid gets set to localized page => must be default language

The patch corrects this behaviour by always set
- the relation (parentid) to the localized page ID
- the page ID (pid) to the default language page ID

Additionally, when adding an Inline element (IRRE) via AJAX
on page properties, the PID gets resolved correctly to be sent
to DataHandler.

Resolves: #82983
Releases: master
Change-Id: Id8bf39524ee6...