Disabled elements are hard to distinguish

Problem/Motivation

It is challenging for sighted users to distinguish between an enabled and disabled url alias field in dark mode on node/add/event.

Discussed and iterated on the issue with @mgifford, @the_g_bomb, @katannshaw, and @drupa11y

Steps to reproduce

• Go to node/add/event, expand the URL alias detail element, and toggle the Generate automatic URL alias switch on and off.

Proposed resolution

• It is not a WCAG failure, but the current case could be improved by simply applying progressive disclosure. If the Gin switch for generating automatic URL aliases is active, hide the text field since it is disabled anyway, while when the Gin switch is inactive, show the text field since the user is supposed to be able to enter an URL alias.
• It is another reminder to write up an issue for core to finally deal with disabled elements by simply applying the aforementioned progressive disclosure or in case progressive disclosure is inapplicable make the component informal removing the visual affordance (for example by removing the caret on select element instead of making components semi-transparent).

Remaining tasks

User interface changes

API changes

Data model changes