mini.files: add an option to mark unsaved/modified files

[Myrrrca]

When browsing files with mini.files it is impossible to see which files have modified/unsaved changes.
A visual indicator (such as a different color or an icon) for modified files would greatly improve usability. Having an option to set this as a parameter in .setup() would be nice. I can open a PR if you dont mind merging it as a feature

[echasnovski]

That's an interesting idea!

Luckily, this can be implemented relatively concisely with already present 'mini.files' capabilities. For example with something like this:

-- Track which files are modified
local modified_files = {}
local register_modified = function(ev) modified_files[ev.match] = vim.bo[ev.buf].modified end
vim.api.nvim_create_autocmd('BufModifiedSet', { callback = register_modified })

-- Highlight file system entry in red if its file is modified
local my_highlight = function(fs_entry)
  if modified_files[fs_entry.path] then return 'DiagnosticError' end
  return MiniFiles.default_highlight(fs_entry)
end
require('mini.files').setup({ content = { highlight = my_highlight } })