GDScript: Add support for relative paths in load()

[dalexeev]

• Fixes load doesn't work for relative paths that go back a folder without "res://" #35832.
• See also Fix GDScript load with relative path #66550 (comment).
• See also Inconsistent treatment of load() from relative path #90029.
• See also [Doc] Document loading behavior with relative paths #90039.

TODO

• Add tests.
• Update docs.

[AThousandShips]

I think this could be a great improvement, but some questions and things to clarify in the documentation bit:

• Is this determined on a script by script basis, i.e. not by the scene the script is used in, if it is, or the location of a resource using the script, i.e. if you have res://a/foo.gd and save a resource of that resource as res://b/bar.tres, and in a method in foo.gd there's a load("baz.png"), does it load res://a/baz.png or res://b/baz.png?
• If yes, how does it work with inheritance, I.e. if you create a script res://b/bar.gd which extends some script res://a/foo.gd, how does it handle the question above?

Just some things I think would be easy traps for people depending on how it works, so would be important to document clearly

[dalexeev]

I think the behavior should be identical to preload(), except for load() is executed at runtime. I.e. path is relative to the directory in which the current script is located.

[lyuma]

Does this handle edge cases in which the load or ResourceLoader.load functions are called dynamically?

For example, if I pass a reference to the ResourceLoader.load function using .bind(), or if I use .call_deferred("load", ...) vs .load.call_deferred(...), those will not work with relative paths I assume?

Also what happens if a user who does not use ResourceLoader declares their own func load(filename: String) in script?