[Editor] Unload addons before quitting to allow cleanup.

[bruvzg]

Fixes #92727

Adds extra plugin unloading step before deleting scene tree to ensure plugins can use the same code for both unloading and disabling plugin.

Existing documentation suggest freeing stuff, including removing nodes in the _exit_tree, which can't be done if plugin is unloaded during scene tree deletion. While removing nodes manually is not necessary, unloading other resources might be, and it is needed to handle disabling plugins, doing all of it from the _exit_tree probably is more convenient than separate _disable_plugin and resource cleanup.

[MikeSchulze]

A question, when it is now triggered _disable_plugin at Godot exit than it should also trigger _enable_plugin at Godot editor start right?

[bruvzg]

A question, when it is now triggered _disable_plugin at Godot exit than it should also trigger _enable_plugin at Godot editor start right?

It's not triggering _disable_plugin on exit (nor _enable_plugin on start).

• on start it triggers _enter_tree
• on exit _exit_tree
• when plugin enabled from project settings _enter_tree and then _enable_plugin
• when plugin disabled from project settings _disable_plugin and then _exit_tree

So with this change, all cleanups can go to _exit_tree.

[akien-mga]

Thanks!

[bruvzg]

For the reference: this broke custom importer add-ons (fix #93518). Since this is a case, it might affect some other plugin processes as well (I have not found any other issues so far).

[kitbdev]

EditorNode::_exit_editor isn't called when using --import or --quit command line flags, so the problem still exists in that case. Maybe NOTIFICATION_EXIT_TREE would be a better place?