Raise C++ standard to C++20

[ranisalt]

Pull Request Prelude

• I have followed proper The Forgotten Server code styling.
• I have read and understood the contribution guidelines before making this PR.
• I am aware that this PR may be closed if the above-mentioned criteria are not fulfilled.

Changes Proposed

Raise the required C++ standard from C++17 to C++20. It has the following benefits (not exhaustive):

• Potentially improved compile times using concepts instead of SFINAE for code where we use std::enable_if
• More expressive code through the use of ranges (not range-for), views and spans
• Native std::format that can replace fmt
• constexpr if and consteval to perform more work during compile time
• Coroutines, which can help writing generator functions where we currently generate a whole container of items before processing it (e.g. recursively navigating a container)

See more language features and compiler support.

Minimum compiler version with decent C++20 support is gcc 8 and clang 6, with gcc 9 and clang 8 being mostly feature-complete.

[Erza]

Native std::format that can replace fmt

I wish. Last time I checked a few months ago, GCC still didn't support std::format. I switched to C++20 on a project because I wanted to use it, and then found out that GCC still did not support the C++20 text formatting at the end of 2022....

GCC 13 finally supports it now, but it's not even released yet.

[ranisalt]

GCC 13 finally supports it now, but it's not even released yet.

It's just wishful thinking. We will still use libfmt, since we use colors, but maybe one day std::format matures enough :P hopefully the rest of the reasons are appealing enough

[ArturKnopik]

Please update <LanguageStandard>stdcpp17</LanguageStandard> to <LanguageStandard>stdcpp20</LanguageStandard> in theforgottenserver.vcxproj file

a lot of problems with lambdas, maybe the introduction of the C++20 standard will fix memory leaks by the way (#4288)