bpo-42990: Functions inherit current builtins (GH-24564)

The types.FunctionType constructor now inherits the current builtins
if the globals dictionary has no "__builtins__" key, rather than
using {"None": None} as builtins: same behavior as eval() and exec()
functions.

Defining a function with "def function(...): ..." in Python is not
affected, globals cannot be overriden with this syntax: it also
inherits the current builtins.

PyFrame_New(), PyEval_EvalCode(), PyEval_EvalCodeEx(),
PyFunction_New() and PyFunction_NewWithQualName() now inherits the
current builtins namespace if the globals dictionary has no
"__builtins__" key.

* Add _PyEval_GetBuiltins() function.
* _PyEval_BuiltinsFromGlobals() now uses _PyEval_GetBuiltins() if
  builtins cannot be found in globals.
* Add tstate parameter to _PyEval_BuiltinsFromGlobals().