GDScript: Add some checks for @tool and @icon

[dalexeev]

Closes #76059.

[YuriSizov]

Should probably add tests for those cases.

[dalexeev]

Should probably add tests for those cases.

Done.

[YuriSizov]

Thanks! Btw, why err if a non-global class has an icon? We can still use them in the editor. I even has a PR adding support for those.

[dalexeev]

I even has a PR adding support for those.

At least it doesn't currently work. This is even written in the docs, but there is no check in the parser.

Add a custom icon to the current script. The script must be registered as a global class using the class_name keyword for this to have a visible effect.

Btw, why err if a non-global class has an icon?

Probably because the editor reads this data from the .godot/global_script_class_cache.cfg file that only contains global named classes.

[YuriSizov]

Yes, in my PR I add a way to get it directly from the script.

#75656

[dalexeev]

Yes, in my PR I add a way to get it directly from the script.

Okay, then I will remove that part. I will not delete the obsolete note in the docs, please do it within #75656.

[aaronfranke]

I think this check is a good idea, even though it is fixing a very minor problem.

[aaronfranke]

this-> is redundant but it's consistent with the below, so I guess it's OK.

[akien-mga]

Thanks!