C++ source files should include only C++ wrappers over C headers instead of plain C headers

[cflaviu]

Examples:

• <cstdint> instead of <stdint.h>
• <cassert> instead of <assert.h>

[avdgrinten]

I think this is not necessary in the general case (it doesn't add anything but adds a bit of code churn). There are several cases where C++ headers are needed because they add functionality though: for example, <cstddef> adds std::byte and nullptr_t.

We control the C headers anyway, so there is little reason to replace them by C++ headers.

[cflaviu]

Well I guess in the future those C++ headers will be needed anyway. It's more a matter of time from my point of view.

[avdgrinten]

Sure, when we need functionality, we will switch. But replacing all C style headers now doesn't have any advantage.