Bug 31558: Fix image drag and drop in TinyMCE

Bug 31558: Fix image drag and drop in TinyMCE

Bug 26949 upgraded JS lib TinyMCE to 5.9.2

This version has a known issue on images drag and drop :
https://stackoverflow.com/questions/64782955/tinymce-inline-drag-and-drop-image-upload-not-working

Test plan :
1) Go to Tools > HTML customizations
2) Create a new entry (not using text editor)
3) Drag and drop an image
=> Without patch you see an error message from TinyMCE 'Dropped file type is not supported'
=> With patch : It works !

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>