Updated PR documentation:
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The types.FunctionType constructor now inherits the current builtins
if the globals parameter is used and the globals dictionary has no
"__builtins__" key, rather than rather than using {"None": None} as
builtins: same behavior than 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.
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This PR makes FunctionType makes more consistent with other Python functions.

Also, it doesn't prevent people to attempt building a "sandbox", it remains possible to override __builtins__ in FunctionType, eval(), exec(), etc.

Usally, such sandbox pass a modified builtins namespace to eval() and exec() and the functions simply inherit it, functions defines with "def function(...): ..." and functions created with types.FunctionType constructor: my PR only impacts a very specific case, when types.FunctionType is called with a different globals dictionary which has no "__builtins__" key.