GDExtension: Pass count when freeing method and property lists for script instances

[dsnopek]

Currently, the free_property_list and free_method_list functions on GDExtensionScriptInstanceInfo2 don't accept the number of items in the list. Since the GDExtension probably allocated memory for each item in the list, it will need to loop over all the elements in the list in order to free that memory.

In order to work around this, all existing GDExtensions that provide a scripting language do some sort of hack to save the list count. For example, the Luau bindings allocate the list with some extra room at the front to stash the count and then do some pointer math:

https://github.com/Fumohouse/godot-luau-script/blob/69d5e02fc1e94101cf31d7bd9b384ad2423cdd96/src/luau_script.h#L222

In any case, none of these hacks or workarounds would be necessary if Godot simply passed the count to the free_property_list and free_method_list functions, which is what this PR does!

(In addition to these changes, I also wrapped more of the code to support deprecated structs in ScriptInstanceExtension with #ifndef DISABLE_DEPRECATED to make builds without deprecated code a little lighter.)

[AThousandShips]

Code looks good and the feature makes sense

[dsnopek]

Thinking about this a little more, I think now that the ScriptInstanceExtension::deprecated_native_info struct contains multiple function pointers, it would probably make sense to dynamically allocate it, so that all ScriptInstanceExtensions (including those that don't use the deprecated pointers) don't get larger.

I'll update this PR to do that a little later.

[dsnopek]

I just pushed the changes to dynamically allocate the deprecated native info struct!

I re-tested this with the Luau GDExtension, using the older interface, and everything still seems to be working.

[akien-mga]

Thanks!