CEF C++ wrapper requires C++14 features starting with M93

[Marshall Greenblatt]

The CEF C++ wrapper (libcef_dll_wrapper) and related CEF header files have been updated to require C++14 features starting with current master and the M93 release branch. This impacts C++ users only as the CEF C API remains unchanged.

To support these features the minimum client build toolchain requirements for C++ have been updated as follows:

• Visual Studio 2019 or newer.
• GCC 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04) or newer. Older Linux distros are no longer supported starting with M93 as previously announced here.
• Xcode 12.2 to 12.5. These versions require MacOS 10.15.4 (Catalina) or newer, and support both Intel 64-bit and ARM64 builds.

Some changes are also required in C++ client applications when updating to M93 or newer. These changes can be summarized as follows (follow the links for additional details):

• Build with -std=c++14 instead of  -std=gnu++11 on Mac and Linux.
• The scoped_ptr type has been removed. Use std::unique_ptr instead (with std::move, std::make_unique, base::BindOnce, etc).
• The OVERRIDE macro definition has been removed. Use override instead.
• The arraysize macro definition has been removed. Use base::size instead.
• Include include/base/cef_callback.h instead of include/base/cef_bind.h
• Implicit conversion of CefRefPtr<T> or scoped_refptr<T> to T* is gone. Use .get() instead
• The base::Bind() API has been deprecated and will be removed in M94. Use base::BindOnce or base::BindRepeating instead as appropriate.

See issue #3140 for complete details including links to new C++ language features and examples of the code changes that were required when updating the CEF sample applications.