feat(buffers): add buffers_sort option (#2793)

* refactor: add sort_buffers option to buffers picker

* refactor: validate sort_buffers opt is a function

lua/telescope/builtin/__internal.lua

@@ -912,6 +912,10 @@ internal.buffers = function(opts)
     end)
   end
 
+  if type(opts.sort_buffers) == "function" then
+    table.sort(bufnrs, opts.sort_buffers)
+  end
+
   local buffers = {}
   local default_selection_idx = 1
   for _, bufnr in ipairs(bufnrs) do

lua/telescope/builtin/init.lua

@@ -349,6 +349,7 @@ builtin.reloader = require_on_exported_call("telescope.builtin.__internal").relo
 ---@field sort_mru boolean: Sorts all buffers after most recent used. Not just the current and last one (default: false)
 ---@field bufnr_width number: Defines the width of the buffer numbers in front of the filenames  (default: dynamic)
 ---@field file_encoding string: file encoding for the previewer
+---@field sort_buffers function: sort fn(bufnr_a, bufnr_b). true if bufnr_a should go first. Runs after sorting by most recent (if specified)
 builtin.buffers = require_on_exported_call("telescope.builtin.__internal").buffers
 
 --- Lists available colorschemes and applies them on `<cr>`