GDScript: Consolidate behavior for assigning enum types

This makes sure that assigning values to enum-typed variables are
consistent. Same enum is always valid, different enum is always
invalid (without casting) and assigning `int` creates a warning
if there is no casting.

There are new test cases to ensure this behavior doesn't break in
the future.

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

@@ -0,0 +1,10 @@
+enum MyEnum { ENUM_VALUE_1, ENUM_VALUE_2 }
+enum MyOtherEnum { OTHER_ENUM_VALUE_1, OTHER_ENUM_VALUE_2 }
+
+# Different enum types can't be assigned without casting.
+var class_var: MyEnum = MyEnum.ENUM_VALUE_1
+
+func test():
+	print(class_var)
+	class_var = MyOtherEnum.OTHER_ENUM_VALUE_2
+	print(class_var)

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

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+Cannot assign a value of type "MyOtherEnum (enum)" to a target of type "MyEnum (enum)".

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

@@ -0,0 +1,8 @@
+enum MyEnum { ENUM_VALUE_1, ENUM_VALUE_2 }
+enum MyOtherEnum { OTHER_ENUM_VALUE_1, OTHER_ENUM_VALUE_2 }
+
+# Different enum types can't be assigned without casting.
+var class_var: MyEnum = MyOtherEnum.OTHER_ENUM_VALUE_1
+
+func test():
+	print(class_var)

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

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+Value of type "MyOtherEnum (enum)" cannot be assigned to a variable of type "MyEnum (enum)".

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

@@ -0,0 +1,8 @@
+enum MyEnum { ENUM_VALUE_1, ENUM_VALUE_2 }
+enum MyOtherEnum { OTHER_ENUM_VALUE_1, OTHER_ENUM_VALUE_2 }
+
+func test():
+	var local_var: MyEnum = MyEnum.ENUM_VALUE_1
+	print(local_var)
+	local_var = MyOtherEnum.OTHER_ENUM_VALUE_2
+	print(local_var)

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

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+Cannot assign a value of type "MyOtherEnum (enum)" to a target of type "MyEnum (enum)".

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

@@ -0,0 +1,6 @@
+enum MyEnum { ENUM_VALUE_1, ENUM_VALUE_2 }
+enum MyOtherEnum { OTHER_ENUM_VALUE_1, OTHER_ENUM_VALUE_2 }
+
+func test():
+	var local_var: MyEnum = MyOtherEnum.OTHER_ENUM_VALUE_1
+	print(local_var)

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

@@ -0,0 +1,2 @@
+GDTEST_ANALYZER_ERROR
+Value of type "MyOtherEnum (enum)" cannot be assigned to a variable of type "MyEnum (enum)".