We plan on using this for online assets (see blender/blender!130543), to
send status updates with a URL to identify the online library remote.
In future this can be expanded for multiple kinds of messages with
differing data, like progress reports, sub-resource download messages
(e.g. individual assets), etc.
While this will only be used for online assets for the start, I imagine
we'd want these same kind of status messages for other remote
resources. Hence the name `WM_MSG_TYPE_REMOTE_IO`.
Pull Request: https://projects.blender.org/blender/blender/pulls/144567
17f1c055da