backports: Copy mkdir_p TOCTOU fix from elixir PR 14242

See: https://github.com/elixir-lang/elixir/pull/14242

changelog.d/toctou-mkdir.fix

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+Backport [Elixir PR 14242](https://github.com/elixir-lang/elixir/pull/14242) fixing racy mkdir and lack of error handling of parent directory creation

lib/pleroma/backports.ex

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+# Copyright 2012 Plataformatec
+# Copyright 2021 The Elixir Team
+# SPDX-License-Identifier: Apache-2.0
+
+defmodule Pleroma.Backports do
+  import File, only: [dir?: 1]
+
+  # <https://github.com/elixir-lang/elixir/pull/14242>
+  # To be removed when we require Elixir 1.19
+  @doc """
+  Tries to create the directory `path`.
+
+  Missing parent directories are created. Returns `:ok` if successful, or
+  `{:error, reason}` if an error occurs.
+
+  Typical error reasons are:
+
+    * `:eacces`  - missing search or write permissions for the parent
+      directories of `path`
+    * `:enospc`  - there is no space left on the device
+    * `:enotdir` - a component of `path` is not a directory
+
+  """
+  @spec mkdir_p(Path.t()) :: :ok | {:error, File.posix() | :badarg}
+  def mkdir_p(path) do
+    do_mkdir_p(IO.chardata_to_string(path))
+  end
+
+  defp do_mkdir_p("/") do
+    :ok
+  end
+
+  defp do_mkdir_p(path) do
+    parent = Path.dirname(path)
+
+    if parent == path do
+      :ok
+    else
+      case do_mkdir_p(parent) do
+        :ok ->
+          case :file.make_dir(path) do
+            {:error, :eexist} ->
+              if dir?(path), do: :ok, else: {:error, :enotdir}
+
+            other ->
+              other
+          end
+
+        e ->
+          e
+      end
+    end
+  end
+
+  @doc """
+  Same as `mkdir_p/1`, but raises a `File.Error` exception in case of failure.
+  Otherwise `:ok`.
+  """
+  @spec mkdir_p!(Path.t()) :: :ok
+  def mkdir_p!(path) do
+    case mkdir_p(path) do
+      :ok ->
+        :ok
+
+      {:error, reason} ->
+        raise File.Error,
+          reason: reason,
+          action: "make directory (with -p)",
+          path: IO.chardata_to_string(path)
+    end
+  end
+end