Copy-pasting content with images from a page in view mode to a page in wysiwyg edit mode adds images from attachments as external URL images

Steps to reproduce:

• create a page A in your wiki
• edit the page and add a paragraph and an image
• save and view
• open another page B in your wiki, in edit mode
• copy the paragraph + image from page A in view mode
• paste this into the wysiwyg editor of page B
• save
• page B now looks exactly like page A

Expected result:

• page B also has the image of page A as an attachment

Actual result:

• the image on page B is added as an external URL image, pointing to the attachments of page A but not as a wiki reference but as an external URL
• thus, page A doesn't have any knowledge that there are some other pages on the wiki referring its attachments
  • if page A is moved or deleted, the image on page B will be broken

Note that this is different from issue XWIKI-15350 in the fact that that issue is talking about copying between 2 open editors while this issue is about copying between a page in view mode and a page in edit mode.
The behaviour of XWIKI-15350 is actually "good" in the sense that it allows the editor to realize that something is not exactly as it should about their copy-paste, and maybe re-upload the image on page B. In the usecase of this issue it looks like it's all fine and the job was done as expected.