Draft: DO NOT MERGE: Resolve #3396718 "D10 source plugins"

This adds Drupal 10 support for the Source plugins.

This should not be merged! It's only to support projects upgrading to Drupal 10 that are using the Lingotek Overrides Source plugins.

• This is a followup to this MR: !13 (closed)
• This MR is created on top of changes introduced in this MR. !19 (merged). (commit: a372ccf4)
• This only works with a patched version of Lingotek 3.8.1. That patch is added to support Drupal 10 on Lingotek 3.8.1 lingotek-3.8.1-drupal-10.patch

To get this working:

1. Apply this patch to lingotek 3.8.1: lingotek-3.8.1-drupal-10.patch
2. composer require drupal/lingotek_overrides (should be commit a372ccf4)
3. Add composer patches:

    "drupal/lingotek_overrides": {
      "3396718: D10 support - Introduce plugin type for data sources": "https://git.drupalcode.org/project/lingotek_overrides/-/merge_requests/20.diff",
    },

For some more context:

Lingotek overrides has two approaches for extending translation functionality: Source Plugins and FieldProcessor plugins. The former was an early attempt at implementing that feature and is now deprecated in favor of FieldProcessor plugins since they are more aligned with the way Lingotek proper works. However there are some projects that still rely on the Source plugins. This MR refactors work in the original MR (linked above) so that it can work with Drupal 10. It does not introduce any new features