The compositor backdrop is still visible even after a new completely
different file is loaded. This is because compositor contexts cache
things like the backdrop, and contexts are stored on interactive
compositor renders, which are not freed until Blender is closed. To fix
this, we cleanup the interactive compositor renders that were created
upon file load.
Pull Request: https://projects.blender.org/blender/blender/pulls/135390
a50144e55c