Clean up threading.pyi (#6525)

- Adds comments to aliases in the `threading` module to indicate that they're deprecated.
- Adds two missing aliases, for consistency.
- Closes #6494

stdlib/threading.pyi

@@ -11,8 +11,9 @@ _T = TypeVar("_T")
 __all__: list[str]
 
 def active_count() -> int: ...
+def activeCount() -> int: ...  # deprecated alias for active_count()
 def current_thread() -> Thread: ...
-def currentThread() -> Thread: ...
+def currentThread() -> Thread: ...  # deprecated alias for current_thread()
 def get_ident() -> int: ...
 def enumerate() -> list[Thread]: ...
 def main_thread() -> Thread: ...
@@ -55,14 +56,15 @@ class Thread:
     def start(self) -> None: ...
     def run(self) -> None: ...
     def join(self, timeout: float | None = ...) -> None: ...
-    def getName(self) -> str: ...
-    def setName(self, name: str) -> None: ...
     if sys.version_info >= (3, 8):
         @property
         def native_id(self) -> int | None: ...  # only available on some platforms
     def is_alive(self) -> bool: ...
     if sys.version_info < (3, 9):
         def isAlive(self) -> bool: ...
+    # the following methods are all deprecated
+    def getName(self) -> str: ...
+    def setName(self, name: str) -> None: ...
     def isDaemon(self) -> bool: ...
     def setDaemon(self, daemonic: bool) -> None: ...
 
@@ -102,7 +104,7 @@ class Condition:
     def wait_for(self, predicate: Callable[[], _T], timeout: float | None = ...) -> _T: ...
     def notify(self, n: int = ...) -> None: ...
     def notify_all(self) -> None: ...
-    def notifyAll(self) -> None: ...
+    def notifyAll(self) -> None: ...  # deprecated alias for notify_all()
 
 class Semaphore:
     def __init__(self, value: int = ...) -> None: ...
@@ -121,6 +123,7 @@ class BoundedSemaphore(Semaphore): ...
 class Event:
     def __init__(self) -> None: ...
     def is_set(self) -> bool: ...
+    def isSet(self) -> bool: ...  # deprecated alias for is_set()
     def set(self) -> None: ...
     def clear(self) -> None: ...
     def wait(self, timeout: float | None = ...) -> bool: ...