GDScript: Treat enum values as int and enum types as dictionary

Since enums resolve to a dictionary at runtime, calling dictionary
methods on an enum type is a valid use case. This ensures this is true
by adding test cases. This also makes enum values be treated as ints
when used in operations.

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

@@ -0,0 +1,21 @@
+# Enum is equivalent to int for comparisons and operations.
+enum MyEnum {
+	ZERO,
+	ONE,
+	TWO,
+}
+
+enum OtherEnum {
+	ZERO,
+	ONE,
+	TWO,
+}
+
+func test():
+	print(MyEnum.ZERO == OtherEnum.ZERO)
+	print(MyEnum.ZERO == 1)
+	print(MyEnum.ZERO != OtherEnum.ONE)
+	print(MyEnum.ZERO != 0)
+
+	print(MyEnum.ONE + OtherEnum.TWO)
+	print(2 - MyEnum.ONE)

modules/gdscript/tests/scripts/analyzer/features/enum_is_treated_as_int.out

@@ -0,0 +1,7 @@
+GDTEST_OK
+true
+false
+true
+false
+3
+1

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

@@ -0,0 +1,13 @@
+enum MyEnum {
+	ZERO,
+	ONE,
+	TWO,
+}
+
+func test():
+	for key in MyEnum.keys():
+		prints(key, MyEnum[key])
+
+	# https://github.com/godotengine/godot/issues/55491
+	for key in MyEnum:
+		prints(key, MyEnum[key])

modules/gdscript/tests/scripts/analyzer/features/enum_type_is_treated_as_dictionary.out

@@ -0,0 +1,7 @@
+GDTEST_OK
+ZERO 0
+ONE 1
+TWO 2
+ZERO 0
+ONE 1
+TWO 2