Fixed #14760 - Admin inlines with file/image field fails to save_as

https://github.com/django/django/pull/697 reworked for master.

Refactored BaseInlineFormSet and ModelAdmin to copy initial
values (file name) for fields of FileField or it's subclasses.

'physical' file do not get duplicated.
Maybe you can explain this as to why the logic is repeat both here and in the formset. Overall, this seems a bit hacky to me.