Problem: Message lines from multiple message events that end up
spilling 'cmdheight' end up spread out over the cmdline
and "more" window.
Messages emitted as feedback to a typed :command (rather than
its sole purpose like :echo/:=) are routed to the more window.
The more window isn't closed when entering the cmdwin, and
doesn't allow `vim.hl.on_yank()`.
Solution: When first opening the "more" window for spilled messages,
move the message buffer to the more window.
Restrict routing of typed commands to echo kinds.
Ignore all events but WinLeave and TextYankPost.
ff95d7ff9a