bpo-39529: Deprecate creating new event loop in asyncio.get_event_loop() (GH-23554)

asyncio.get_event_loop() emits now a deprecation warning when it creates a new event loop.
In future releases it will became an alias of asyncio.get_running_loop().
diff --git a/Doc/library/asyncio-task.rst b/Doc/library/asyncio-task.rst
index 1ca1b4a..3f54ecb 100644
--- a/Doc/library/asyncio-task.rst
+++ b/Doc/library/asyncio-task.rst
@@ -397,6 +397,11 @@
       If the *gather* itself is cancelled, the cancellation is
       propagated regardless of *return_exceptions*.
 
+   .. deprecated:: 3.10
+      Deprecation warning is emitted if no positional arguments are provided
+      or not all positional arguments are Future-like objects
+      and there is no running event loop.
+
 
 Shielding From Cancellation
 ===========================
@@ -434,6 +439,10 @@
        except CancelledError:
            res = None
 
+   .. deprecated:: 3.10
+      Deprecation warning is emitted if *aw* is not Future-like object
+      and there is no running event loop.
+
 
 Timeouts
 ========
@@ -593,6 +602,10 @@
            earliest_result = await coro
            # ...
 
+   .. deprecated:: 3.10
+      Deprecation warning is emitted if not all awaitable objects in the *aws*
+      iterable are Future-like objects and there is no running event loop.
+
 
 Running in Threads
 ==================
@@ -775,6 +788,10 @@
    .. deprecated-removed:: 3.8 3.10
       The *loop* parameter.
 
+   .. deprecated:: 3.10
+      Deprecation warning is emitted if *loop* is not specified
+      and there is no running event loop.
+
    .. method:: cancel(msg=None)
 
       Request the Task to be cancelled.