Add separate depth setting for folder browser

[giodueck]

Is your feature request related to a problem? Please describe.
Since #419 and #420, a certain workflow has broken for me which I found to be useful as it was before, although - I agree - inconsistent in its configuration.

It is no longer convenient to have the file browser have the depth of 1 and use the folder browser to quickly jump to a nested directory, because the depth setting then affects the file browser which looks cluttered.

To make the folder browser useful as a quick navigation tool, I find depth necessary, and to make the file browser useful, I find depth annoying.

Describe the solution you'd like
Could the depth be separated into two options? I.e. add a new one for the folder browser.

Describe alternatives you've considered
I have tried creating distinct mappings for opening the file browser in file and in folder modes, but since selecting a directory in folder mode enables the file mode the depth option applies to this mode.

Is there a way to add a hook to listen to <CR> in the picker? Then I could try setting the depth option dynamically.

[giodueck]

As a workaround, to get back the behavior as it was before, I created a function that hacks at the options for the current picker:

-- Sets depth to 1 and selects default
local reset_depth_select_default = function(prompt_bufnr)
  local picker = require('telescope.actions.state').get_current_picker(prompt_bufnr)
  picker.finder.depth = 1
  require('telescope.actions').select_default(prompt_bufnr)
end

This is then the function that I call on <CR>:

require('telescope').setup {
  defaults = {--[[ snip ]]},
  pickers = {--[[ snip ]]},
  extensions = {
    file_browser = {
      hijack_netrw = true,
      mappings = {
        ["i"] = {
          ["<CR>"] = reset_depth_select_default,
        },
        ["n"] = {
          ["<CR>"] = reset_depth_select_default,
        },
      },
    },
  },

Now when opening the folder browser with an arbitrary depth (e.g. 4) and selecting a directory, it toggles the file browser after setting depth = 1.

Could be more sophisticated, but this fits my need for now.

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If this is good enough to avoid creating a new config option, I'm fine with just closing this issue.