bpo-45188: Windows now regenerates frozen modules at the start of build instead of...

bpo-45188: Windows now regenerates frozen modules at the start of build instead of late (GH-28322)

This will enable us to drop the frozen module header files from the repository.

It does currently cause many source files to be built twice, which just takes more time. For whoever comes to fix this in the future, the files shared between freeze_module and pythoncore should be put into a static library that is consumed by both.