Simplify script paths to ensure proper resource path checks

[rsubtil]

Fixes #87094.

Prevents script paths that could have partial dirs in them (e.g. res://./addons/<...> or res://folder1/../folder2/<...>) by simplifying them.

This issue manifested on a very specific case (#87094) of an addon with warnings, treating warnings as errors, and a script being supplied through the CLI interface with a preceding ./. It caused the script path to become res://./addons/..., which then fails this check and erroneously lets the warning be issued:

godot/modules/gdscript/gdscript_parser.cpp

Lines 184 to 186 in 26b1fd0

	if (GLOBAL_GET("debug/gdscript/warnings/exclude_addons").booleanize() && script_path.begins_with("res://addons/")) {
	return;
	}

If applying this fix to the script_path is risky, I can move it to this check instead.

[akien-mga]

Thanks!

[akien-mga]

Thanks!

[akien-mga]

Thanks!