Fixes T5849. When a new file is created, we might have to actually write the data to a storage engine, or we might be able to just point at data which is already there.

Currently, these two paths handle $params with different code and mild behavioral differences. Instead, have them call the same code so they get the same behavior.

• Uploaded the same file multiple times to home page.
• Uploaded the same file multiple times as profile picture.
• Generated files via Diffusion.
• All the files got the expected properties, whether they were reusing data or not.