feature request: Filter files (e.g. according to file extension)

[FrancisH-C]

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• I have searched the existing issues

Describe the feature

I'd like a way to filter and show files with a given file extension.

Provide background

I wanted to sort file according to file extension as in #224.
Filtering files is, for me (and maybe others), a good alternative. It seems easier to implement.

What is the significance of this feature?

nice to have

Additional details

Being new to lua, my current solution is to have a keybinding to do

function()
  local oil = require("oil")
  local filter = vim.fn.input("Fitler")

  local is_hidden_file = function(name, bufnr)
    local m = name:match(filter)
    return m ~= nil
  end

  -- Set the custom function to determine if a file is hidden
  oil.set_is_hidden_file(is_hidden_file)
end

I'd like an "official" way of doing it with the following "constraint":

1. Easy to toggle on and off
2. toggle_hidden should not be affect by the filter (at least when turned off)
3. Specify files to show not the ones to hide

Thank you for Oil