Add drush 10 support

@andypost: is that only there is needed?

Yep. Works for me with Drush 10.2.2.

It works out of the box for me without this patch:

drush 10.3.5
drupal 8.9.7

I can't remember if the patch was necessary for it to work in Drush 10.2 or not (I think it was?), but I just tested it again in Drush 10.3.4, and it does indeed work without the patch.

From https://www.drush.org/commands/#specifying-the-services-file:

In Drush 10, however, the services section must exist, and must name the services file to be used. If a future Drush extension is written such that it only works with Drush 10 and later, then its entry would read "drush.services.yml": "^10", and Drush 9 would not load the extension's commands. It is all the same recommended that Drush 9 extensions explicitly declare their services file with an appropriate version constraint.

RTBC++

This change may have broken our tests, there was a commit made November 4th that broke our tests. see the following issues and links:

4 Nov 2020 at 04:27 EST

PHP 7.1 & MySQL 5.5, D8.9 Composer require failure

18 Sep 2019 at 10:45 EDT

PHP 7.1 & MySQL 5.5, D8.7 242 pass

Other changes that were made November 4th that may have caused this:

#3165948: License "GPL-2.0+" is a deprecated SPDX license identifier, use "GPL-2.0-or-later" instead

#2598934: Hook_Array warning on upgrade attempt

#3081813: Add drush 10 support

fix automated tests, broken with changes made November 4th 2020

#3183927: Fix automated tests, broken since November 4th 2020

Proposed resolution / Remaining Tasks

make a patch that reverts all changes made november 4th and see if it fixes the tests.

The tests appear to be passing again.