Rollup merge of #65961 - lcnr:typename_of, r=Dylan-DPC

Rollup merge of #65961 - lcnr:typename_of, r=Dylan-DPC

add fn type_name_of_val

This function is often useful during testing and mirrors `align_of_val` and `size_of_val`.

# Example

Showing the default type of integers.

```rust
let x = 7;
println!("per default, integers have the type: {}", std::any::type_name_of_val(&x));
```

To my knowledge this can currently not be done without defining a function similar to `type_name_of_val`.