Support for UI Skins theme setting

Thanks a lot for the feature request and the MR.

I will give a look and test.

Can we move...

The declaration in some YAML files?

in order to be authorable by front developers.

For example, naive proposal in ui_suite_bootstrap.ui_skins.themes:

# No target because scopable.
# No value because same as plugin ID.
dark:
  label: "Dark"
  label_context: "color"
  key: "data-bs-theme"
  bg_utility:
    - bg-dark
  fg_utility:
    - text-bg-dark

# No target because scopable.
# No value because same as plugin ID.
light:
  label: "Light"
  label_context: "color"
  key: "data-bs-theme"
  utility_equivalent:
    - bg-light
    - text-bg-light

The Bootstrap::getThemeMapping() logic in UI Skins?

We can keep the apply in the ui_suite_bootstrap PHP code for now, so those function will call the new UI Skins API:

• PreprocessPage::preprocess()
• PreprocessMediaMediaLibrary::preprocess()
• FormMediaLibraryAddFormAlter
• ElementPreRenderLayoutBuilder

UI Skins issue created ✨ Theme definition: link to utility classes Active .

I will isolate generic stuff unrelated to theme selection in another MR to merge it right now.

Merged what was independent from UI Skins.

First MR rebased, so it is clearer what needs to be made generic.

Postponing until UI Skins issue is done.

Seems like just removing the specific light classes is enough for the dark theme support!