Enforce that custom nodes and resources created via the "Create New Node" dialog, should permanently retain their original type (script). This means:
- Type continuity: It should be impossible for the user to (accidentally) clear the original script of a custom node that was created via the "Create New Node" dialog.
- Extensibility: The user should be able to extend custom types as usual (create a script that inherits the original type and replace the original script of that node with his own). However, if he then clears his extension-script from that node later on, the custom type should revert to its original script instead of becoming a non-scripted type.
Since the same argument is used, `SceneState::get_node_deferred_nodepath_properties()`
should use similar logic to `SceneState::get_property_value()`.
Make `SceneState::get_property_value()` to return whether the property is deferred.
This allows to include script_instance.h directly in the
generated gdvirtual.gen.inc, and remove excessive includes
from the codebase.
This should also allow Resource to use GDVIRTUAL macros,
which wasn't possible previously due to a circular dependency.
As many open source projects have started doing it, we're removing the
current year from the copyright notice, so that we don't need to bump
it every year.
It seems like only the first year of publication is technically
relevant for copyright notices, and even that seems to be something
that many companies stopped listing altogether (in a version controlled
codebase, the commits are a much better source of date of publication
than a hardcoded copyright statement).
We also now list Godot Engine contributors first as we're collectively
the current maintainers of the project, and we clarify that the
"exclusive" copyright of the co-founders covers the timespan before
opensourcing (their further contributions are included as part of Godot
Engine contributors).
Also fixed "cf." Frenchism - it's meant as "refer to / see".
