gh-89653: PEP 670: Convert unicodeobject.h macros to functions (#92648)

Convert the following Unicode macros to static inline functions.

Surrogate functions:

* Py_UNICODE_IS_SURROGATE()
* Py_UNICODE_IS_HIGH_SURROGATE()
* Py_UNICODE_IS_LOW_SURROGATE()
* Py_UNICODE_HIGH_SURROGATE()
* Py_UNICODE_LOW_SURROGATE()
* Py_UNICODE_JOIN_SURROGATES()

"Is" functions:

* Py_UNICODE_ISALNUM()
* Py_UNICODE_ISSPACE()

In the implementation of these functions, the character type is now
well defined to Py_UCS4.