[clang-tools-extra] [clang-tidy] add modernize-use-constexpr check (PR #146553)

[Sean McBride via cfe-commits]

seanm wrote:

Another interesting case, it seems somehow multiple constexprs got added, ex:

```c++
template <typename CellType>
constexpr constexpr constexpr constexpr constexpr constexpr constexpr constexpr int numberOfSidesOfDimension(int dimension);
```

This actually compiles, though with a `-Wduplicate-decl-specifier` warning.

https://github.com/llvm/llvm-project/pull/146553