Persistent mark names don't propagate to other active vim instances

[Yilin-Yang]

As above.

• Suppose that there's a global mark 'Z.
• We open vim instance (1), which shows mark 'Z in its markbar.
• We open vim instance (2), which also shows mark 'Z in its markbar.
• In (1), we give 'Z the user-set name "foobar". This name is shown in (1)'s markbar, but not shown in (2)'s markbar.
• If we close (2) and then open a new vim instance (3), then the name "foobar" will show up in its markbar.