[Meta] Move module.theme.css files to Classy or Seven

• Issue summary needs updating as it is targeting themes that have been removed
• It should be determined if this is even still desirable because:
  • There is now libraries_extends and libraries_override
  • Enough time has passed that this might not be desirable for Drupal anymore. This needs to be verified before moving further
  • Even if there are benefits to the approach, we also have to recognize that it would be disrupting something that has been in place for nearly 10 years. Are the benefits worth that disruption?

There's following files in 10.1 core

./core/themes/stable9/css/toolbar/toolbar.icons.theme.css
./core/themes/stable9/css/toolbar/toolbar.theme.css
./core/themes/stable9/css/contextual/contextual.icons.theme.css
./core/themes/stable9/css/contextual/contextual.theme.css
./core/themes/stable9/css/taxonomy/taxonomy.theme.css
./core/themes/stable9/css/views_ui/views_ui.admin.theme.css
./core/themes/stable9/css/content_moderation/content_moderation.theme.css
./core/themes/stable9/css/settings_tray/settings_tray.theme.css
./core/themes/stable9/css/shortcut/shortcut.theme.css
./core/themes/stable9/css/shortcut/shortcut.icons.theme.css
./core/themes/stable9/css/update/update.admin.theme.css
./core/themes/claro/css/theme/views_ui.admin.theme.css
./core/themes/claro/css/theme/toolbar.icons.theme.css
./core/themes/claro/css/theme/filter.theme.css
./core/themes/claro/css/theme/tour.theme.css
./core/themes/claro/css/theme/toolbar.theme.css
./core/themes/olivero/css/theme/filter.theme.css
./core/modules/toolbar/css/toolbar.icons.theme.css
./core/modules/toolbar/css/toolbar.theme.css
./core/modules/system/tests/modules/css_disable_transitions_test/css/disable_transitions.theme.css
./core/modules/contextual/css/contextual.icons.theme.css
./core/modules/contextual/css/contextual.theme.css
./core/modules/taxonomy/css/taxonomy.theme.css
./core/modules/views_ui/css/views_ui.admin.theme.css
./core/modules/content_moderation/css/content_moderation.theme.css
./core/modules/settings_tray/tests/modules/settings_tray_test_css/css/css_fix.theme.css
./core/modules/settings_tray/css/settings_tray.theme.css
./core/modules/shortcut/css/shortcut.theme.css
./core/modules/shortcut/css/shortcut.icons.theme.css
./core/modules/update/css/update.admin.theme.css
./core/profiles/demo_umami/themes/umami/css/components/tour/tour.theme.css

I have to assume the list of files in #81 are there to provide information that moves the issue forward, but I'm unfortunately not sure what that is.