build(aio): refactor dgeni packages

This is to tidy up the `author-packagse`, which currently duplicates a
lot of the configuration in the main packages. We need to
DRY this up so that we don't fall foul of a change in one being missed in
the other.

aio/tools/transforms/angular-content-package/processors/copyContentAssets.js

@@ -0,0 +1,12 @@
+
+module.exports = function copyContentAssetsProcessor(copyFolder) {
+  return {
+    $runAfter: ['files-written'],
+    assetMappings: [],
+    $process() {
+      this.assetMappings.forEach(map => {
+        copyFolder(map.from, map.to);
+      });
+    }
+  };
+};

aio/tools/transforms/angular-content-package/processors/copyContentAssets.spec.js

@@ -0,0 +1,27 @@
+const testPackage = require('../../helpers/test-package');
+const Dgeni = require('dgeni');
+const factory = require('./copyContentAssets');
+
+describe('extractDecoratedClasses processor', function() {
+  let dgeni, injector, processor;
+
+  beforeEach(function() {
+    dgeni = new Dgeni([testPackage('angular-content-package')]);
+    injector = dgeni.configureInjector();
+    processor = injector.get('copyContentAssetsProcessor');
+  });
+
+  it('should exist', () => {
+    expect(processor).toBeDefined();
+  });
+
+  it('should call copyFolder with each mapping', () => {
+    const mockCopyFolder = jasmine.createSpy();
+    processor = factory(mockCopyFolder);
+    processor.assetMappings.push({ from: 'a/b/c', to: 'x/y/z' });
+    processor.assetMappings.push({ from: '1/2/3', to: '4/5/6' });
+    processor.$process();
+    expect(mockCopyFolder).toHaveBeenCalledWith('a/b/c', 'x/y/z');
+    expect(mockCopyFolder).toHaveBeenCalledWith('1/2/3', '4/5/6');
+  });
+});