CEF C++ wrapper requires C++20 features starting with M145

[Marshall Greenblatt]

The CEF C++ wrapper (libcef_dll_wrapper) and related CEF header files will require C++20 features starting with current master and the M145 release branch. This impacts C++ users only as the CEF C API remains unchanged.

Minimum supported compiler versions for C++20 are:

• Visual Studio 2019 16.9.3 [unchanged]
• GCC 10 (Ubuntu 20) [previously: GCC 7.5.0]
• Clang 16 (Xcode 16.0) [previously: Clang 12 (Xcode 12.2)]

Build configurations will need to be updated as follows:

• Build with -std=c++20 instead of -std=c++17 on MacOS and Linux.
• Build with /std:c++20 instead of /std:c++17 on Windows.

See issue #3611 for complete details.