[Feature] Support mini.icon library

[pidgeon777]

Is your feature request related to a problem? Please describe.
This icons library was released recently:

https://github.com/echasnovski/mini.icons

It seems to be better than:

https://github.com/nvim-tree/nvim-web-devicons

Describe the solution you'd like
It would be great if lspsaga.nvim also could support the mini.icons library.

Describe alternatives you've considered
None

Additional context
The mini.icons library has already been integrated into popular Neovim distributions such as LazyVim, with great results.

[stevenxxiu]

Here's a way to patch this for now:

config = function(_, opts)
  -- Patch to use *mini.icons*
  require('lspsaga.util').icon_from_devicon = function(ft) return require('mini.icons').get('filetype', ft) end

  require('lspsaga').setup(opts)
end,

It'll be better to make this a config option of course, like in bufferline's options.get_element_icon. bufferline supplies the arguments: directory, extension, filetype, path, type.