[clang-tools-extra] [clang-tidy] New bugprone-unsafe-format-string check (PR #168691)

[Daniel Krupp via cfe-commits]

dkrupp wrote:

> > maybe bugprone-unbounded-format-string ?
> 
> Sounds good to me

I can imagine a checker extension that checks if the destination buffer is larger than limiter size specified in the format string.
e.g. 
```
char buffer[10]
scanf("%99s",buffer) //warn unsafe string 
```
So for now I would leave the checker name as is (bugprone-unsafe-format-string) to allow extensibility for other cases.

@vbvictor, @zwuis  What do you think?

https://github.com/llvm/llvm-project/pull/168691