Dropdown improvements

## Hidden content is not searchable
Content inside collapsed dropdowns is not searchable using browser-native search (cmd+f / ctrl+f). This negatively impacts usability, especially on pages with long lists of items hidden in dropdowns because users are unable to easily find the content they are looking for.

For example: https://www.elastic.co/docs/reference/query-languages/esql/esql-functions-operators
Using cmd+f to search for a specific function name does not work unless the dropdown containing that content is already expanded.

Proposal:
Ensure dropdown content is discoverable via browser search. Possible approaches:
- Render all dropdown content in the DOM by default (even if visually collapsed)
- Use accessible disclosure patterns (e.g., / tags)
- Explore JavaScript solutions that temporarily expand all dropdowns during a search

## Dropdowns all collapsed by default
When a user lands on a page with multiple dropdowns, all sections are collapsed. This makes it unclear that the page contains expandable sections and can lead to confusion or missed content.

Proposal:
Automatically expand the first dropdown section on page load. This provides a visual cue that other sections can be expanded, helping users understand the interaction model of the page.