Problem:
:LspInfo has its own "inner platlform" of highlights, mappings etc. And
it doesn't integrate with :checkhealth.
Solution:
- Move the lspinfo code to a healthcheck.
- LspInfo features such as highlights, "floating window" presentation,
etc., should be added to :checkhealth in Nvim core, if they are really
needed.
- Define a "q" mapping until Nvim stable has that in :checkhealth.
Problem:
Users/plugins may want to use the config definition without actually
activating the config via setup().
Solution:
- Expose `config_def` field and document it.
- Also undeprecate some stuff that doesn't yet have a documented
alternative.
TODO: configs.lua sets `M.filetypes = config.filetypes` and other fields
in ad-hoc fashion "for :LspInfo" but it's not clear when those fields
are actually populated, and they don't source from `config_def`...
