vendor a part of distutils, to be removed from stdlib in py3.12

distutils (a module in the python standard library that we use) got deprecated in python 3.10,
and is planned to be removed from the stdlib in python 3.12.
see 9d38120e33/Lib/distutils/__init__.py (L16)
We only use it in the Qt update_checker (for signed version notifications), to compare version numbers.
That is, we only use a very small part of it (only `distutils.version.StrictVersion`).

```
.../electrum/electrum/gui/qt/update_checker.py:7: DeprecationWarning: The distutils package is deprecated and slated for removal in Python 3.12. Use setuptools or check PEP 632 for potential alternatives
  from distutils.version import StrictVersion
```

Migration advice in PEP-632 suggests ( https://peps.python.org/pep-0632/#migration-advice ):
> `distutils.version` — use the `packaging` package

Note that `packaging` is a 3rd party package, i.e. it would be a new dependency.
Also, it does not provide an identical replacement for `distutils.version.StrictVersion`.

Care needs to be taken when changing the semantics of version numbers...
E.g. `packaging.parse` and `packaging.Version` are less strict than what we currently use.
We have to be careful that old code recognises new electrum version numbers as both valid
and numerically greater than their version.

I think the easiest approach is for us to vendor this small part of distutils.
Re directory structure, this is based on `pip`:
bab5bfce50/src/pip/_vendor
(although the approach here is much more naive ofc)

electrum/gui/qt/update_checker.py

@@ -4,7 +4,6 @@
 
 import asyncio
 import base64
-from distutils.version import StrictVersion
 
 from PyQt5.QtCore import Qt, QThread, pyqtSignal
 from PyQt5.QtWidgets import (QWidget, QVBoxLayout, QLabel, QProgressBar,
@@ -17,6 +16,7 @@ from electrum.i18n import _
 from electrum.util import make_aiohttp_session
 from electrum.logging import Logger
 from electrum.network import Network
+from electrum._vendor.distutils.version import StrictVersion
 
 
 class UpdateCheck(QDialog, Logger):