Include filetypes from `filetypes.lua` in checks

[gegoune]

Not all filetypes will have syntax files (I think), so while checking for missing filetypes in https://github.com/nvim-tree/nvim-web-devicons/blob/master/scripts/filetypes.sh#L10-L20 we should, on top of presence of syntax/<filetype>, check $VIMRUNTIME/lua/vim/filetype.lua as well.

[alex-courtis]

That looks like it feeds new API vim.filetype.match. I am wary, though, as this will vary based on vim version etc.

I'm keen on generating this list at startup time, based on the filetypes that are actually available. Less maintenance.

[gegoune]

What's the risk of defining filetype mapping for filetype that does not exist for user/their version of nvim?

[alex-courtis]

What's the risk of defining filetype mapping for filetype that does not exist for user/their version of nvim?

I don't think there's any issue; it's only ever looked up as a map with the user provided filetype:

function M.get_icon_name_by_filetype(ft)
  return filetypes[ft]
end