Problem: Calling :redraw from vim.ui_attach() callback results in
recursive cmdline/message events.
Solution: Avoid recursiveness where possible and replace global "call_buf"
with separate, temporary buffers for each event so that when a Lua
callback for one event fires another event, that does not result
in invalid memory access.
Just some basic spring cleaning.
In the distant past, not all UI:s where remote UI:s. They still aren't,
but both of the "UI" and "UIData" structs are now only for remote UI:s.
Thus join them as "RemoteUI".
Before, we needed to always pack an entire msgpack_rpc Object to
a continous memory buffer before sending it out to a channel.
But this is generally wasteful. it is better to just flush
whatever is in the buffer and then continue packing to a new buffer.
This is also done for the UI event packer where there are some extra logic
to "finish" of an existing batch of nevents/ncalls. This doesn't really
stop us from flushing the buffer, just that we need to update the state
machine accordingly so the next call to prepare_call() always will
start with a new event (even though the buffer might contain overflow
data from a large event).
Determine the needed buffer space first, instead of trying to revert the
effect of prepare_call if message does not fit. The previous code did
not revert the full state, which caused corrupted messages to be sent.
So, rather than trying to fix all of that, with fragile and hard to read
code as a result, the code is now much more simple, although slightly
slower.
Remove `export` pramgas from defs headers as it causes IWYU to believe
that the definitions from the defs headers comes from main header, which
is not what we really want.
