Cleanup Civi markup to use the 'canonical' style-guide versions

The hoped-for final step of the theme project is to cleanup Civi markup to remove the multitude of patterns found in #56, repolacing them with the canonical versions specified in #57, so that the theme #58 can shrink in size/complexity.

The further the project of replacing Civi's Admin UI screens with SearchKit and FormBuilder gets, the smaller this task becomes.

Edited Sep 20, 2023 by nicol

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