UI: Fix imported scene collection names duplicating

If an imported scene collection has a name that already exists, it will
instead be given a name plus an increment (e.g. "name 2", or "name 3",
etc)

Fixes obsproject/obs-studio#4442

UI/window-basic-main-scene-collections.cpp

@@ -73,7 +73,7 @@ void EnumSceneCollections(std::function<bool(const char *, const char *)> &&cb)
 	os_globfree(glob);
 }
 
-static bool SceneCollectionExists(const char *findName)
+bool SceneCollectionExists(const char *findName)
 {
 	bool found = false;
 	auto func = [&](const char *name, const char *) {