build(ngc): run integration test hermetically

This ensures we run in a clean directory, using our real distribution. It finds bugs like @internal
APIs needed to type-check in the offline compiler, as well as problems in package.json.

Also move tsc-wrapped under tools/@angular

tools/broccoli/broccoli-typescript.ts

@@ -3,7 +3,7 @@ import fse = require('fs-extra');
 import path = require('path');
 import * as ts from 'typescript';
 import {wrapDiffingPlugin, DiffingBroccoliPlugin, DiffResult} from './diffing-broccoli-plugin';
-import {MetadataCollector} from '../tsc-wrapped';
+import {MetadataCollector} from '../@angular/tsc-wrapped';
 
 type FileRegistry = ts.Map<{version: number}>;