[BUGFIX] Expose import file in BeforeImportEvent

The file being about to be imported is
now exposed in the BeforeImportEvent.

This information might be quite relevant for
event listeners to decide about modifications
to the `Import` instance.

Resolves: #102657
Releases: main, 12.4
Change-Id: I03c2493b7beda4d07e17d1112117d090f0fae545
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82122


Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>