Ensure that dropzonejs properly validates uploads before creating a file

Incorporated the fix from ✨ Add support to create new taxonomy terms (entities) during bulk upload Needs review into this issue since it also required support for entity validations of the created entity references.

Seems similar to or duplicate of:

📌 Add form validation to inform other module to valid the new uploaded files Fixed

which is much simpler. I haven't reviewed this code yet though.

@codebymikey Would you please provide your thoughts on differences with the other issue?

This implementation is a little more verbose, but only because it tries as much as possible to make all the same API calls a normal File upload would normally call (e.g. all the dropzone-isms with \Drupal\dropzonejs\DropzoneJsUploadSave::createFile ensuring that the uploaded files with potential executable extensions are still properly escaped and validated as seen fit by whichever UploadSave service the site is choosing to run).

This variation also needed to support validation on the Media entity level as well which that version didn't.

Rerolled the patch.

I assume this is ready for review so changing status.