bpo-43244: Rename pycore_ast.h functions to _PyAST_xxx() (GH-25252)

Rename AST functions of pycore_ast.h to use the "_PyAST_" prefix.
Remove macros creating aliases without prefix. For example, Module()
becomes _PyAST_Module(). Update Grammar/python.gram to use
_PyAST_xxx() functions.
9 files changed