bpo-35059: Add Py_STATIC_INLINE() macro (GH-10093)

* Add Py_STATIC_INLINE() macro to declare a "static inline" function.
  If the compiler supports it, try to always inline the function even if no
  optimization level was specified.
* Modify pydtrace.h to use Py_STATIC_INLINE() when WITH_DTRACE is
  not defined.
* Add an unit test on Py_DECREF() to make sure that
  _Py_NegativeRefcount() reports the correct filename.