Allow C++20 features in CEF binary distribution code

[magreenblatt]

Issue #3362 added support for C++17 features and changed the build configuration on Mac/Linux to -std=c++17. We should now consider support for C++20 (-std=c++20) which was recently allowed for use in Chromium code.

Current minimum supported compiler versions for C++17 are:

• Visual Studio 2019 16.9.3 - C++ support documentation
• GCC 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04) - C++ support documentation
• Clang 12 (Xcode 12.2) - C++ support documentation

Proposed minimum supported compiler versions for C++20 are:

• Visual Studio 2019 16.9.3 [unchanged]
• GCC 9 (Ubuntu 20.04) [may require newer]
• Clang 15 (Xcode 15.0) [may allow older]