Fix GDScript base and outer classes, signals and functions lookup order

- Add outer class lookup test
- Add signal lookup test

Co-authored-by: Dmitrii Maganov <vonagam@gmail.com>

modules/gdscript/tests/scripts/analyzer/features/lookup_class.gd

@@ -0,0 +1,50 @@
+# Inner-outer class lookup
+class A:
+    const Q: = "right one"
+
+class X:
+    const Q: = "wrong one"
+
+class Y extends X:
+    class B extends A:
+        static func check() -> void:
+            print(Q)
+
+# External class lookup
+const External: = preload("lookup_class_external.notest.gd")
+
+class Internal extends External.A:
+    static func check() -> void:
+        print(TARGET)
+
+    class E extends External.E:
+        static func check() -> void:
+            print(TARGET)
+            print(WAITING)
+
+# Variable lookup
+class C:
+    var Q := 'right one'
+
+class D:
+    const Q := 'wrong one'
+
+class E extends D:
+    class F extends C:
+        func check() -> void:
+            print(Q)
+
+# Test
+func test() -> void:
+    # Inner-outer class lookup
+    Y.B.check()
+    print("---")
+
+    # External class lookup
+    Internal.check()
+    Internal.E.check()
+    print("---")
+
+    # Variable lookup
+    var f: = E.F.new()
+    f.check()