[BUGFIX] Display relations' titles when TCA label field is type inline

This change adds a case to treat "inline" TCA types the same way
"select" is treated when building the record's label value.

Before, if record used field of type "inline" as TCA label field, TYPO3
would display fx "3" (number of related records as stored in field
on parent record).

After, TYPO3 will display fx "Record1, Record2, Record2" if "inline"
field contains three related records named thusly.

Fixes: #52133
Releases: 6.2, 6.1, 6.0, 4.7, 4.5
Change-Id: Ie06f09368e81505cb1e5989b61ae98add54b05ba
Reviewed-on: https://review.typo3.org/23911
Reviewed-by: Markus Klein
Tested-by: Markus Klein