Add sys.getfilesystemencodeerrors from PEP 529 (#4864)

stdlib/3/sys.pyi

@@ -160,6 +160,7 @@ if sys.platform != "win32":
     def getdlopenflags() -> int: ...
 
 def getfilesystemencoding() -> str: ...
+def getfilesystemencodeerrors() -> str: ...
 def getrefcount(__object: Any) -> int: ...
 def getrecursionlimit() -> int: ...
 @overload