python#8440: Update parameter types in complex.__new__

For two-parameter overload:
 - Change first parameter to complex | SupportsComplex | SupportsFloat
 - Change second parameter to complex | SupportsFloat (Python doesn't allow SupportsComplex for the second parameter, though it isn't clear why)
 - Add SupportsIndex to both parameters for Python >= 3.8
For one-parameter overload:
 - Remove SupportsIndex for Python < 3.8

Author: smlerman

stdlib/builtins.pyi

@@ -364,10 +364,17 @@ class float:
     def __bool__(self) -> bool: ...
 
 class complex:
-    @overload
-    def __new__(cls: type[Self], real: float = ..., imag: float = ...) -> Self: ...
-    @overload
-    def __new__(cls: type[Self], real: str | SupportsComplex | SupportsIndex | complex) -> Self: ...
+    if sys.version_info >= (3, 8):
+        # Python doesn't currently accept SupportsComplex for the second argument
+        @overload
+        def __new__(cls: type[Self], real: complex | SupportsComplex | SupportsFloat | SupportsIndex = ..., imag: complex | SupportsFloat | SupportsIndex = ...) -> Self: ...
+        @overload
+        def __new__(cls: type[Self], real: str | SupportsComplex | SupportsIndex | complex) -> Self: ...
+    else:
+        @overload
+        def __new__(cls: type[Self], real: complex | SupportsComplex | SupportsFloat = ..., imag: complex | SupportsFloat = ...) -> Self: ...
+        @overload
+        def __new__(cls: type[Self], real: str | SupportsComplex | complex) -> Self: ...
     @property
     def real(self) -> float: ...
     @property