gh-93453: No longer create an event loop in get_event_loop() (#98440)

asyncio.get_event_loop() now always return either running event loop or
the result of get_event_loop_policy().get_event_loop() call. The latter
should now raise an RuntimeError if no current event loop was set
instead of creating and setting a new event loop.

It affects also a number of asyncio functions and constructors which
call get_event_loop() implicitly: ensure_future(), shield(), gather(),
etc.

DeprecationWarning is no longer emitted if there is no running event loop but
the current event loop was set.

Co-authored-by: Łukasz Langa <lukasz@langa.pl>

Lib/asyncio/futures.py

@@ -77,7 +77,7 @@ class Future:
         the default event loop.
         """
         if loop is None:
-            self._loop = events._get_event_loop()
+            self._loop = events.get_event_loop()
         else:
             self._loop = loop
         self._callbacks = []
@@ -413,7 +413,7 @@ def wrap_future(future, *, loop=None):
     assert isinstance(future, concurrent.futures.Future), \
         f'concurrent.futures.Future is expected, got {future!r}'
     if loop is None:
-        loop = events._get_event_loop()
+        loop = events.get_event_loop()
     new_future = loop.create_future()
     _chain_future(future, new_future)
     return new_future