[BUGFIX] Default image title in RTE contains the file name

When inserting an image in the RTE, the default image title should be
the image file title, not the image file name.

Resolves: #58373
Releases: 6.1, 6.2
Change-Id: I5aa3aae4db83cbd36244b89cc37c78184b290228
Reviewed-on: https://review.typo3.org/29780
Reviewed-by: Stanislas Rolland
Tested-by: Stanislas Rolland