Unify and streamline connecting to Resource changes

[KoBeWi]

Resource's changed signal is one of the most used signals in the codebase. So far there was no standard way to use it, editors and nodes just connected them however they pleased:

• using connect(CoreStringNames::get_singleton()->changed
• using connect(SNAME("changed"
• using connect("changed"

There was also a weird and underused concept of "resource owners". The idea is that you do register_owner(this) and then Resource calls notify_change_to_owners() and you get notified. The problem is that you need to manually register and deregister the resource. Also the callback is a hard-coded "resource_changed" method. On top of that, this mechanism was used in a few 3D-related classes. Some used it instead the changed signal, which made it impossible to listen to changes normally (the resource_changed thing is not exposed). Some classes used both the signal and notify. And then there is ShapeCast3D, which both connected to signal and to the notify, which means that it reacted twice to each change, running the same code in 2 separate methods xd

Another thing is that it's often good practice to use is_connected() before connecting the signal, to avoid errors. This resulted in code like

Callable c= callable_mp()
if (!is_connected(c)) {
    connect(c)
}

or in worse cases the callable was just repeated twice ¯\_( •_•)_/¯

This PR resolves all aforementioned issues by:

• adding connect_changed() and disconnect_changed() methods to Resource, which always connect with CoreStringNames
• both methods first check if the signal is (isn't) already connected, also respecting the CONNECT_REFERENCE_COUNTED flag
• I changed all code to use these methods, which in some cases reduced 4 lines of boilerplate into one
• this also allowed to remove core_string_names include in some files
• resource owners are removed and replaced with the usage of connect_changed() and emit_changed()
• emit_changed() is now public, so it can be called outside the resource (just like in GDScript xdd)

The new methods are not exposed (yet?).

[fire]

Looks good but I only looked at the resource changes.

I can't think of a better design.

Edited:

Some documentation changes needed.

[KoBeWi]

Right, the resource_changed() methods were bound. I guess we could deprecate them 🤔

[KoBeWi]

Ok, the methods were deprecated. They are just callbacks that should be called by the resource, they were never meant to be used in script. I added some generic description.

[seppoday]

Question: Does that PR allow to add "Synchronize Resource Changes" in play mode the same way script and editor changes right now can have effect when game is played? Right now if you change image (resource) you need to reload game. Maybe that PR could be first step to change it?

[KoBeWi]

This PR just makes it easier to connect signals. It might help with implementation, but doesn't make anything new possible.
Note that lack of resource synchronization is a bug, as it used to be supported IIRC.

[YuriSizov]

It makes sense on the surface. Needs a rebase though.

Maybe @reduz can tell us something about the idea behind the owners, but to me it looks like some legacy system that can be safely replaced by signals.

[YuriSizov]

Thanks!

[DarkMessiah]

Is that right?

[KoBeWi]

no .-.

[YuriSizov]

According to a crude regex, these are the only two

(checked for removed lines with ^-(.*)connect\(("changed"|CoreStringNames|SNAME\("changed"), 270 total, 268 matching this regex)

[DarkMessiah]

Here too :)