[llvm] [docs][libFuzzer] Fix formatting and collapsed definition lists (PR #206709)

[Thurston Dang via llvm-commits]

thurstond wrote:

> ## Summary
> This PR fixes broken formatting and collapsed definition lists in the libFuzzer documentation by adding missing blank lines.
> 
> Closes #206706

This message is what would be used as the commit description if merged. "## Summary" would be redundant.

https://github.com/llvm/llvm-project/pull/206709