[build-utils] Add NodejsLambda class (#7423)

When an instance of this class is returned in a Builder's `output`, it is a signal to the build system that it needs to add additional files to the final Lambda before creating the zip file.

packages/build-utils/test/unit.nodejs-lambda.test.ts

@@ -0,0 +1,21 @@
+import { NodejsLambda, FileBlob } from '../src';
+
+describe('Test `NodejsLambda`', () => {
+  it('should create an instance', () => {
+    const helloSrc = 'module.exports = (req, res) => res.end("hi");';
+    const lambda = new NodejsLambda({
+      files: {
+        'api/hello.js': new FileBlob({ data: helloSrc }),
+      },
+      handler: 'api/hello.js',
+      runtime: 'node14.x',
+      shouldAddHelpers: true,
+      shouldAddSourcemapSupport: false,
+    });
+    expect(lambda.handler).toEqual('api/hello.js');
+    expect(lambda.runtime).toEqual('node14.x');
+    expect(lambda.shouldAddHelpers).toEqual(true);
+    expect(lambda.shouldAddSourcemapSupport).toEqual(false);
+    expect(lambda.awsLambdaHandler).toBeUndefined();
+  });
+});