extend modules/Core.json with general information about the Qt build

For example, Qt VS Tools reads from qconfig.pri the following information:

• QT_ARCH
• QT_NAMESPACE
• QT_VERSION

While this works currently, qconfig.pri might not be available anymore in the future.

In the CMake build such information is available in lib/cmake/Qt6Core/Qt6CoreConfigExtras.cmake but reading it would require a CMake parser (or more or less fragile regular expressions).

It would be nice if modules/Core.json would contain this information. A way to read JSON should be ubiquitous.