[clang-tools-extra] [clangd] don't lower severity of clang-tidy modernize-* checks to remarks (PR #75706)

[Nathan Ridge via cfe-commits]

HighCommander4 wrote:

> Explicitly pinging @kadircet and @sam-mccall for your involvement in the mentioned commit. What are your thoughts on this? I looked into this because someone on discord asked about this difference.

Added Sam and Kadir as reviewers.

This patch seems to contradict the explicit motivation of the previous one expressed in this code comment:

```c++
  // We downgrade severity for certain noisy warnings, like deprecated
  // declartions. These already have visible decorations inside the editor and
  // most users find the extra clutter in the UI (gutter, minimap, diagnostics
  // views) overwhelming.
```

I think clang-tidy "modernize" warnings can definitely be noisy in this way.

That said, we've also received feedback that the strike-through style that some editors apply for the `Deprecated` tag is even more distracting than the underline (https://github.com/clangd/vscode-clangd/issues/482).

https://github.com/llvm/llvm-project/pull/75706