Problem: Messages routed to the pager to be shown in full, enter the
pager automatically, yielding another "press-q-prompt".
Solution: Only enter the pager when requested explicitly. Otherwise,
close the pager on the next typed mapping, unless that mapping
entered the pager.
Problem: vim._extui unconditionally creates windows, buffers and the
Vimscript cmdline highlighter when it is first loaded.
Solution: Schedule first creation of the window so that first redraw
happens sooner (still need to create at least the cmdline
window asap as it can have a different highlight through
hl-MsgArea; thus further delaying until the first event that
needs a particular target seems redundant). Load the cmdline
highlighter on the first cmdline_show event.
Problem: ext_messages cannot tell when the screen was cleared, which is
needed to clear visible messages. An empty message is also
never emitted, but clears messages from the message grid.
Solution: Repurpose the "msg_clear" event to be emitted when the screen
was cleared. Emit an empty message with the `empty` kind to
hint to a UI to clear the cmdline area.
Problem: OptionSet autocmd emitted with invalid grids after entering
tabpage with different 'cmdheight'.
Solution: First call `tabpage_check_windows()` before changing 'cmdheight'.
Add a test that exercises the `vim._extui` cmdline.
Problem: UI buffers may be 'unmodifiable' and use a 'swapfile'.
Solution: Set the 'modifiable' and 'noswapfile' options.
Co-authored-by:phanium <91544758+phanen@users.noreply.github.com>
Problem: No ext_messages kind for the :command, :version commands.
:version is emitted as multiple events.
Solution: Assign them the "list_cmd" kind. Use `msg_put*` to properly
format the message as a single event.
