Update version of C++/WinRT to 2.0.201201.7 or later

[vmoroz]

The version 2.0.201201.7 is adopted internally by some Microsoft teams. We should do the update too.
According to @kennykerr it has the following notable changes:

• Many coroutine improvements
• C++20 coroutine conformance
• Clang conformance improvements
• try_capture and try_create_instance helpers (try_capture and try_create_instance cppwinrt#663)
• Improved compile-time and run-time diagnostics
• Add value type support to as() and try_as() (Add value type support to as() and try_as() cppwinrt#695)
• Enable conversion between winrt::clock and std::chrono::system_clock (Enable conversion between winrt::clock and std::chrono::system_clock cppwinrt#698)
• Add multi-threaded collections (Add multi-threaded collections cppwinrt#692)
• Add try_get_activation_factory overloads with class name (add try_get_activation_factory overloads that take the runtimeclass name cppwinrt#769)
• Support boxing delegates

[chrisglein]

I remember there being some things we needed to do to get community modules on the same version otherwise there were issues. @jonthysell where are we with mixed-cppwinrt versions? Is that a problem still? What should our policy be for updating?

[jonthysell]

AFAIK it's not really an issue anymore, as long as the projects are properly set up with the whole $(SolutionDir)\packages setup.

IIRC camera still targets the version used in 0.62, and still works with 0.63 and 0.64, despite their use of a newer version.

And starting with 0.64, my hope is people use react-native-windows-init to create their project, and perhaps later even to partially update it (as I have done to stamp the latest template files), such that modules will get the newer cppwinrt versions too.