session-manager: move files into client-endpoint / client-session subdirs

To clean up space for the new implementation.
The existing code is exclusively for use with the client-endpoint
and client-session factories.

src/modules/meson.build

@@ -139,12 +139,12 @@ pipewire_module_adapter = shared_library('pipewire-module-adapter',
 
 pipewire_module_session_manager = shared_library('pipewire-module-session-manager',
   [ 'module-session-manager.c',
-    'module-session-manager/client-endpoint.c',
+    'module-session-manager/client-endpoint/client-endpoint.c',
-    'module-session-manager/client-session.c',
+    'module-session-manager/client-endpoint/endpoint-stream.c',
-    'module-session-manager/endpoint-link.c',
+    'module-session-manager/client-endpoint/endpoint.c',
-    'module-session-manager/endpoint-stream.c',
+    'module-session-manager/client-session/client-session.c',
-    'module-session-manager/endpoint.c',
+    'module-session-manager/client-session/endpoint-link.c',
-    'module-session-manager/session.c',
+    'module-session-manager/client-session/session.c',
     'module-session-manager/protocol-native.c',
   ],
   c_args : pipewire_module_c_args,