fix(aws-lambda): java - invalid cast for inline LambdaRuntime members (…

…#505)

TypeScript uses inference to determine if a cast to an interface is legal but
strongly-typed languages like Java require that the down-casted class will
explicitly implement the interface.

The JavaRuntime class has static members that are down-casted from JavaRuntime
to a set of interfaces, to allow strong-typing of properties for various Lambda
use cases. These down-casts fail in e.g. Java because JavaRuntime doesn't implement
these interfaces explicitly.

We should add a compile-time check in jsii for such a use case.

Fixes #504

packages/@aws-cdk/aws-lambda/lib/runtime.ts

@@ -9,18 +9,18 @@ export interface LambdaRuntimeProps {
 /**
  * Lambda function runtime environment.
  */
-export class LambdaRuntime {
+export class LambdaRuntime implements InlinableLambdaRuntime, InlinableJavascriptLambdaRuntime {
     public static readonly NodeJS = new LambdaRuntime('nodejs', { supportsInlineCode: true }) as InlinableJavascriptLambdaRuntime;
-    // Using ``as InlinableLambdaRuntime`` because that calss cannot be defined just yet
+    // Using ``as InlinableLambdaRuntime`` because that class cannot be defined just yet
     public static readonly NodeJS43 = new LambdaRuntime('nodejs4.3', { supportsInlineCode: true }) as InlinableJavascriptLambdaRuntime;
     public static readonly NodeJS43Edge = new LambdaRuntime('nodejs4.3-edge');
-    // Using ``as InlinableLambdaRuntime`` because that calss cannot be defined just yet
+    // Using ``as InlinableLambdaRuntime`` because that class cannot be defined just yet
     public static readonly NodeJS610 = new LambdaRuntime('nodejs6.10', { supportsInlineCode: true }) as InlinableJavascriptLambdaRuntime;
     public static readonly NodeJS810 = new LambdaRuntime('nodejs8.10');
     public static readonly Java8 = new LambdaRuntime('java8');
-    // Using ``as InlinableLambdaRuntime`` because that calss cannot be defined just yet
+    // Using ``as InlinableLambdaRuntime`` because that class cannot be defined just yet
     public static readonly Python27 = new LambdaRuntime('python2.7', { supportsInlineCode: true }) as InlinableLambdaRuntime;
-    // Using ``as InlinableLambdaRuntime`` because that calss cannot be defined just yet
+    // Using ``as InlinableLambdaRuntime`` because that class cannot be defined just yet
     public static readonly Python36 = new LambdaRuntime('python3.6', { supportsInlineCode: true }) as InlinableLambdaRuntime;
     public static readonly DotNetCore1 = new LambdaRuntime('dotnetcore1.0');
     public static readonly DotNetCore2 = new LambdaRuntime('dotnetcore2.0');
@@ -48,7 +48,7 @@ export class LambdaRuntime {
  */
 export interface InlinableLambdaRuntime {
     readonly name: string;
-    readonly supportsInlineCode: true;
+    readonly supportsInlineCode: boolean;
 }
 
 /**