Support for <summary><details> in Markdown Preview

[NoTuxNoBux]

What are you proposing?

Collapsible HTML panels in Markdown have their <summary> dropped and aren't actually made collapsible.

Why does this matter?

To have sections with larger amounts of text in Markdown such as logs that aren't immediately important to the reader unless they want 'more details', or because they obstruct the general flow of the text due to their size.

Are there any examples or context?

1. Create a new markdown file.

# Markdown

<details><summary>Hello World</summary>

- Goodbye Cruel World
- Hello Nothingness

</details>

3. Open markdown preview.

This was transformed from #33657.