gh-90868: Adjust the Generated Objects (gh-99223)

We do the following:

* move the generated _PyUnicode_InitStaticStrings() to its own file
* move the generated _PyStaticObjects_CheckRefcnt() to its own file
* include pycore_global_objects.h in extension modules instead of pycore_runtime_init.h

These changes help us avoid including things that aren't needed.

https://github.com/python/cpython/issues/90868