R1:90f9da643d16

Add and use new RemarkupMetadata class

Summary:
Add a new RemarkupMetadata class and use with upload button as well as drag and drop pathways.

With this change, files are now attached automatically to the object. This this could solve
several issues, for example when a person uploads a file but only that author is able to see it.

Ref T15106

Test Plan:
- Drag and drop file, upload file with button. Check that both files are attached with "attachedFilePHIDs" values.
- drop file in a Task description…