Fixes broken Accordion css in 5.72+

From 5.72 CiviCRM accordions don't have the classnames 'crm-accordion-header' or 'crm-accordion-wrapper'. This PR adjusts the CSS output to support both the new details/summary accordions without those classnames, and older extensions & civicrm installs that still use the old header/wrapper classnames.

These changes were described in the document 'changes in 5.69' in December, but perhaps weren't described clearly enough on my part. I've since updated that document to try to be clearer, and am submitting a PR here so all the people using The Island don't have broken accordions/UI after 5.72.

Based on tests in ThemeTests, this MR fixes both. It also seems to fix a regression with 'crm-master-accordion-header' (the 'light' variation) appearing different on expand/collapse.

Before

After