Update components API docs to list new base styles custom CSS properties

[web-padawan]

Describe your motivation

Follow-up from https://github.com/vaadin/web-components/pull/9608#issuecomment-3027343624

When adding base styles, some new custom CSS properties have been introduced (see corresponding PR descriptions for tables of those). While not currently used in Lumo, they still need to be documented.

Describe the solution you'd like

We should list base new custom CSS properties that are available for styling in the API docs.

Describe alternatives you've considered

No response

Additional context

Consider: https://custom-elements-manifest.open-wc.org/analyzer/getting-started/#documenting-your-components

[web-padawan]

I will be adding custom CSS properties tables for now in relevant PRs, e.g.

• [x] accordion - https://github.com/vaadin/web-components/pull/10616
• [x] app-layout - https://github.com/vaadin/web-components/pull/10671
• [x] avatar - https://github.com/vaadin/web-components/pull/10519
• [ ] checkbox - https://github.com/vaadin/web-components/pull/10725
• [x] details - https://github.com/vaadin/web-components/pull/10616
• [x] horizontal-layout - https://github.com/vaadin/web-components/pull/10422
• [x] popover - https://github.com/vaadin/web-components/pull/10617
• [x] progress-bar - https://github.com/vaadin/web-components/pull/10634
• [x] rich-text-editor - https://github.com/vaadin/web-components/pull/10568
• [x] scroller - https://github.com/vaadin/web-components/pull/10433
• [x] split-layout - https://github.com/vaadin/web-components/pull/10657
• [x] tabs - https://github.com/vaadin/web-components/pull/10637
• [x] tabsheet - https://github.com/vaadin/web-components/pull/10637
• [x] tooltip - https://github.com/vaadin/web-components/pull/10617
• [x] upload - https://github.com/vaadin/web-components/pull/10579
• [x] vertical-layout - https://github.com/vaadin/web-components/pull/10422
• [x] virtual-list - https://github.com/vaadin/web-components/pull/10433