Apply round of code quality improvements from Rector

[paul-m]

Use Drupal-Rector to do the following:

• PHP 8.0 set list to add nice things like str_starts_with(), etc.
• Find ‘dead code’, which means unused variables, easy return short-circuits, etc.
• The Drupal 10 set list, which does things like ensure the $modules variable is protected in tests, etc.

Currently excludes data_dictionary_widget to avoid merge issues.

[dafeder]

This looks good. I think we'll hold off on merging till we have a 2.17 release ready, which will include PHP 8.2 support and dropping PHP 7.4

[dafeder]

Ready I think. Just one thing, I think the title/commit message is a little unclear. Can we make it something like "Apply round of code quality improvements from Rector" or something?