Add automated test for "Automatic link creation when dropping a non-image file"

The manual test is here: Automatic link creation when dropping a non-image file

Existing automated coverage

• RealtimeWYSIWYGEditorIT#dragAndDropFilesAtTheSameTime: Drops non-image files (.webm, .mp4) in the standalone realtime editor (without waiting for the upload notification); asserts attach: links to the dropped files in the source.
• ImageIT#dropFileWithRestrictedMimetype: Drop path with a refused mimetype: warning notification and empty Attachments tab (negative case only).

Missing automated coverage

• Edit a page in-place and drop a non-image file (e.g. PDF or text) over the editing area.
• Assert the "File successfully uploaded." notification (RichTextAreaElement#dropFile(path) with wait already does this).
• Assert a link labelled with the file name is shown in edit mode.
• Save; assert the view page shows a link to the attachment named after the file.
• Assert the file is listed in the Attachments tab.

Suggested location: xwiki-platform-core/xwiki-platform-edit/xwiki-platform-edit-test/xwiki-platform-edit-test-docker/src/test/it/org/xwiki/edit/test/ui/InplaceEditIT.java

Found by comparing the XWiki 18.4.4 manual test runs against the automated tests on master (a0055f10a1a).