[clang] [clang-tools-extra] [clangd] Show struct fields and enum members in hovers (PR #89557)

[Nathan Ridge via cfe-commits]

HighCommander4 wrote:

> I'm planning to revise the patch to make the following changes:
> 
>    1. Put the new behaviour behind a config option (I'm thinking `Hover` --> `ShowFields`)
>    2. Add C language mode tests
>    3. Use `PrintingCallbacks` instead of a `PrintingPolicy` flag

These changes have been made in the latest version of the patch.

https://github.com/llvm/llvm-project/pull/89557