vcpkg port 1.8 fixes

[trueqbit]

In order to update vcpkg's sqlite-orm port, a few things needed to be addressed:

• pinned appveyor test environment to vcpkg 2023.01.09
• made type_is_nullable<> a specializable struct again
• examples are now fully linkable again: chrono_binding.cpp, nullable_enum_binding.cpp, pointer_passing_interface.cpp (those examples wrongly commented out the main() function)
• updated unit test framework to Catch2 v3 (Compile error: catch2 too old #1114)
• updated clang-format lint action on github
• removed dangling submodule reference ("Fetch Content" doesn't work because of catch2-src #1107)
• made all examples compilable with Visual C++ 2015 Update 3

Update (2023-01-15):
Currently unit tests fail with Visual C++ 2015 Update 3 as the minimal C++14 base compiler, as Catch2 v3 now requires a fully compliant C++14 compiler. Let's see what the decision is on the [feature request] (catchorg/Catch2#2624) I made.

Update (2023-01-24):
Now that Catch2 v3 requires a conforming C++14 compiler, legacy compilers like Visual C++ 2015 Update 3 can't be used anymore for compiling the unit tests. The library itself and its examples are still usable with legacy compilers.

[fnc12]

how do you repro a bug which requires this macro? IDK how to do that and that's why I forget to put it sometimes

[trueqbit]

Unfortunately, NSDMI is a core capability of a compiler, so you have to compile it with a compiler that does not have it.
Anyway, I suggest that the v1.8 band is the last one in which we support pre-C++14 compilers. As you may have noticed, Martin Hořeňovský, the maintainer of Catch2, is not interested in maintaining compatibility. So the problem is that it is becoming more and more expensive to maintain compatibility on our side.

[fnc12]

got it. Yes I agree with dropping pre-C++14 compilers support from next releases