Add a splash popup while starting up

Sometimes it can take quite a while to start up and initialise the debug
adapter. So we use popup/float to display the status as we start up and
shut down.

This increases minimum Vim version to 8.2, but that's been out for ages
now and I intend to agressively require latest/later vim/neovim
versions.

tests/ci/image/Dockerfile

@@ -27,7 +27,7 @@ RUN ln -fs /usr/share/zoneinfo/Europe/London /etc/localtime && \
 ## cleanup of files from setup
 RUN rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
-ARG VIM_VERSION=v8.1.1270
+ARG VIM_VERSION=v8.2.0460
 
 ENV CONF_ARGS "--with-features=huge \
                --enable-python3interp \