Using latest feature on neovim 0.5.0 for diagnostics highlights

[chemzqm]

WARING if you're using neovim 0.5.0, make sure you have upgraded it to latest 0.5.0.

Diagnostics highlights update now use nvim_buf_get_extmarks with details to diff current highlights with upcoming highlights, this helps to improve user experience. Check the code at

coc.nvim/autoload/coc/highlight.vim

Line 159 in 05fb7ab

let markers = nvim_buf_get_extmarks(a:bufnr, ns, 0, -1, {'details': v:true})

For performance reason, we've also limited maximum highlights of buffer by diagnostic.highlighLimit configuration, which default to 1000, there would be no highlights for diagnostics exceed that limit.