JetBrains: Extract SearchResultHeader and SelectableSearchResult components and clean up CSS

Created by: philipp-spiess

Closes #36155 (closed) Closes #36154 (closed) Part-of #36703 (closed)

This PR contains a bunch of cleanups of the search result list React components in preparation of #36703 (closed). This includes:

• Extraction of a SelectableSearchResult and a SearchResultHeader wrapper component that applies the styling for, well, selectable rows and unelectable (header) rows.
• Copy SearchResult.module.scss for every sub-type and eliminate unused CSS classes to clean up the styling.

Test plan

The changes were tested locally so there shouldn't be any regressions (but even if, this is just the ground work for more styling related changes soon so it's not a big deal)

Here's an obligatory screenshot but since this is not based on the reference design in Figma, 🤷

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.