fix(kernel): correctly serialize enum values

When string-valued enums were serialized, an incorrect reference would
be created if the label of the enum entry did not match it's string
value; due to the lookup code being incorrect.

Updated a string-valued enum and introduced new compliance tests to
ensure such enum values are passed across correctly.

Fixes #753

packages/jsii-calc/lib/compliance.ts

@@ -27,9 +27,23 @@ export enum AllTypesEnum {
 }
 
 export enum StringEnum {
-    A = 'A',
-    B = 'B',
-    C = 'C'
+    A = 'A!',
+    B = 'B?',
+    C = 'C.'
+}
+
+export class EnumDispenser {
+    public static randomStringLikeEnum(): StringEnum {
+        // Haha! I lied, it's not random!! *EVIL LAUGHTER*
+        return StringEnum.B;
+    }
+
+    public static randomIntegerLikeEnum(): AllTypesEnum {
+        // Haha! I lied, it's not random!! *EVIL LAUGHTER*
+        return AllTypesEnum.YOUR_ENUM_VALUE;
+    }
+
+    private constructor() { }
 }
 
 /**