Couldn't find these in other task, some minor UI tweaks that would be helpful

• Rename "Default" library to something like "User Library". "Default" is not very descriptive.
• Make the library enum button wider, "Current File" barely fits.
• In the library enum menu, don't use two columns but rather just a separator line. Then you would also get rid of the "Custom" title, which I don't really like using. Maybe a single "Libraries" title would help users to identify what this menu contains, since there is not label next to the button.
• In the outliner right click menu, put Mark Asset / Clear Asset together with separators around them, not mixed with the other datablock operations. I think these are quite distinct things.
• Add Mark Asset / Clear Asset to the new datablock dropdown menu.