[3.14] pythongh-131591: Add Py_ prefix to MAX_SCRIPT_PATH_SIZE; remove unprefixed struct tag (pythonGH-135924) (pythonGH-135969)

Names/macros defined in public headers should have `Py`/`_Py` prefixes.
(cherry picked from commit a1da208)

Co-authored-by: Petr Viktorin <[email protected]>

Author: miss-islington