[clang-tools-extra] [clang-tidy] Add `llvm-formatv-string` (PR #195974)

[Dave Lee via cfe-commits]

kastiglione wrote:

I'm running this against llvm, and it surfaced a bug:

```
/Users/dlee43/src/llvm-project/llvm/lib/Support/BalancedPartitioning.cpp:25:17: warning: invalid replacement index in format string [llvm-formatv-string]
   25 |   OS << formatv("{{ID={0} Utilities={{{1:$[,]}} Bucket={2}}", Id,
      |                 ^
```

The index parsing breaks on `{1:$[,]}`. I'll have to make updates to the PR.

https://github.com/llvm/llvm-project/pull/195974