Add type stub for dropped in BoundedList/BoundedDict (#1725)

Author: manojpandey

opentelemetry-sdk/src/opentelemetry/sdk/util/__init__.pyi

@@ -40,6 +40,7 @@ class BoundedList(Sequence[_T]):
     not enough room.
     """
 
+    dropped: int
     def __init__(self, maxlen: int): ...
     def insert(self, index: int, value: _T) -> None: ...
     @overload
@@ -59,6 +60,7 @@ class BoundedDict(MutableMapping[_KT, _VT]):
     added.
     """
 
+    dropped: int
     def __init__(self, maxlen: int): ...
     def __getitem__(self, k: _KT) -> _VT: ...
     def __setitem__(self, k: _KT, v: _VT) -> None: ...