[BUGFIX] Set correct PID for inline elements on page object

The getDefaultUploadFolder hook must get the PID for the current
page if the inline element is located on a page object.

The logic is now as follows:
- In case of records that are stored on a page, $pid is the uid of
that page (pid of the record)
- In case of an existing page $pid is the current page uid
- In case of a new page, $pid is the relative page id as used in other
places (for example -224 for a page below page id 224) - this allows
hook implementations to react accordingly

Resolves: #82881
Releases: master, 9.5
Change-Id: Ie8570f9656f54e25bfec3224411a5014c396ed2e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/54513


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>