Tools (export(tool=True)) do not reload on save

[matheus2740]

I have a tool script (created with export(tool=True)).
When I make changes to the script, and save, I get the following error:

ERROR: set_path: Another resource is loaded from path 'res://worldgen/WorldGen.py' (possible cyclic resource inclusion).
   At: core/resource.cpp:81.
ERROR: reload: Condition "!p_keep_state && _instances.size()" is true. Returned: ERR_ALREADY_IN_USE
   At: modules/gdnative/pluginscript/pluginscript_script.cpp:232.

I then have to restart the editor in order for my tool to update.

[matheus2740]

this appears to be: godotengine/godot#10946

The solution seems to be:
use the gdnative c++ and create a PluginScript subclass, like the ECMAScript guys are doing. See: https://github.com/Geequlim/ECMAScript/blob/master/ecmascript.h

This way we can override PluginScript::reload and remove the line ERR_FAIL_COND_V(!p_keep_state && _instances.size(), ERR_ALREADY_IN_USE); which is preventing the reload.

We could also simplify the logic in this method, and only call importlib.reload.