GDScript: Fix parsing default parameter values from function calls

modules/gdscript/tests/scripts/analyzer/errors/params_default_forward_reference.gd

@@ -0,0 +1,9 @@
+# https://github.com/godotengine/godot/issues/56702
+
+func test():
+	# somewhat obscure feature: referencing parameters in defaults, but only earlier ones!
+	ref_default("non-optional")
+
+
+func ref_default(nondefault1, defa=nondefault1, defb=defc, defc=1):
+	prints(nondefault1, nondefault2, defa, defb, defc)

modules/gdscript/tests/scripts/analyzer/errors/params_default_forward_reference.out

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+Identifier "defc" not declared in the current scope.