correctly map to connection_user from remote_user in play_context (#28676)

This change will map the remote_user prop to connection_user if it is
not aleady set.  It also adds a var mapping to ansible_connection_user
in the inventory to override the local user if needed.  This is
primarily used by the network_cli connection plugin today.

fixes #26120

lib/ansible/playbook/play_context.py

@@ -75,6 +75,7 @@ MAGIC_VARIABLE_MAPPING = dict(
 
     # networking modules
     network_os=('ansible_network_os', ),
+    connection_user=('ansible_connection_user',),
 
     # ssh TODO: remove
     ssh_executable=('ansible_ssh_executable', ),
@@ -494,8 +495,8 @@ class PlayContext(Base):
         # if the final connection type is local, reset the remote_user value to that of the currently logged in user
         # this ensures any become settings are obeyed correctly
         # we store original in 'connection_user' for use of network/other modules that fallback to it as login user
-        # this needs to be done before the MAGIC_VARIABLE_MAPPING happens
         if new_info.connection == 'local':
+            if not new_info.connection_user:
                 new_info.connection_user = new_info.remote_user
             new_info.remote_user = pwd.getpwuid(os.getuid()).pw_name