Rollup merge of #122157 - dpaoliello:targetdesc, r=Nilstrieb

Add the new description field to Target::to_json, and add descriptions for some MSVC targets

The original PR to add a `description` field to `Target` (<rust-lang/rust#121905>) didn't add the field to `Target::to_json`, which meant that the `check_consistency` testwould fail if you tried to set a description as it wouldn't survive round-tripping via JSON: https://github.com/rust-lang/rust/actions/runs/8180997936/job/22370052535#step:27:4967

This change adds the field to `Target::to_json`, and sets some descriptions to verify that it works correctly.

Author: matthiaskrgr