SceneTree.new() causes wrong tree to be shown in the remote view

[Demindiro]

Godot version:
3.2.3.stable.custom_build.31d0f8ad8

OS/device including version:
Linux pc 4.19.0-12-amd64 #1 SMP Debian 4.19.152-1 (2020-10-18) x86_64 GNU/Linux

Issue description:
When creating a new SceneTree with SceneTree.new(), the remote tree view in the editor shows the layout of the new tree instead of the singleton. This happens because of a missing check in the code that assigns the tree in the remote view.

godot/scene/main/scene_tree.cpp

Lines 2134 to 2141 in c43b2ab

	if (ScriptDebugger::get_singleton()) {
	if (ScriptDebugger::get_singleton()->is_remote()) {
	ScriptDebuggerRemote *remote_debugger = static_cast<ScriptDebuggerRemote *>(ScriptDebugger::get_singleton());
	remote_debugger->set_scene_tree(this);
	}
	ScriptDebugger::get_singleton()->set_multiplayer(multiplayer);
	}

Steps to reproduce:

1. Create a node and add the following script:

extends Node

var tree_a := SceneTree.new()

2. Run the project.
3. Check the Remote View. There will only be a root node visible and not the node with the script.

Minimal reproduction project:
multi-scenetree.zip

[ShadyChibinko]

I recently ran into this issue in 3.4.4.stable and it can seriously break the debugging workflow when working with multiple scene trees. More often than not you're creating additional scene trees to run some kind of sub simulation that you've already ironed out prior through the default scene tree. So having the remote inspector display them makes little to no sense. It's also just apparent that this is unintended.

Judging by the code snippet for scene_tree.cpp, I'd assume the fix is as simple as adding a getter for ScriptDebuggerRemote's scene_tree property as defined here:

godot/scene/debugger/script_debugger_remote.h

Line 124 in 419e713

SceneTree *scene_tree;

Then in the scene_tree.cpp block:

godot/scene/main/scene_tree.cpp

Lines 2126 to 2132 in 419e713

	if (ScriptDebugger::get_singleton()) {
	if (ScriptDebugger::get_singleton()->is_remote()) {
	ScriptDebuggerRemote *remote_debugger = static_cast<ScriptDebuggerRemote *>(ScriptDebugger::get_singleton());
	remote_debugger->set_scene_tree(this);
	}
	ScriptDebugger::get_singleton()->set_multiplayer(multiplayer);

You would gate off the line remote_debugger->set_scene_tree(this); with an if statement checking for a null return value from the aforementioned getter. I don't know exactly how the debugger works behind the scenes, but I'd like to think this is plausible.

It's also worth noting that this solution would likely be 3.x only, as Godot 4 seems to have removed the debugger calls above from scene_tree.cpp's constructor entirely.