feat(@ngtools/webpack): allow to pass in overrides for compilerOptions

Close angular#4851

Author: filipesilva

packages/@ngtools/webpack/README.md

@@ -37,6 +37,8 @@ The loader works with the webpack plugin to compile your TypeScript. It's import
 * `mainPath`. Optional if `entryModule` is specified. The `main.ts` file containing the bootstrap code. The plugin will use AST to determine the `entryModule`.
 * `skipCodeGeneration`. Optional, defaults to false. Disable code generation and do not refactor the code to bootstrap. This replaces `templateUrl: "string"` with `template: require("string")` (and similar for styles) to allow for webpack to properly link the resources.
 * `typeChecking`. Optional, defaults to true. Enable type checking through your application. This will slow down compilation, but show syntactic and semantic errors in webpack.
+* `exclude`. Optional. Extra files to exclude from TypeScript compilation.
+* `compilerOptions`. Optional. Override options in `tsconfig.json`.
 
 ## Features
 The benefits and ability of using [`@ngtools/webpack`](https://www.npmjs.com/~ngtools) standalone from the Angular CLI as presented in [Stephen Fluin's Angular CLI talk](https://youtu.be/uBRK6cTr4Vk?t=6m45s) at Angular Connect 2016:

packages/@ngtools/webpack/src/plugin.ts

@@ -32,6 +32,7 @@ export interface AotPluginOptions {
 
   // Use tsconfig to include path globs.
   exclude?: string | string[];
+  compilerOptions?: ts.CompilerOptions;
 }
 
 
@@ -113,6 +114,14 @@ export class AotPlugin implements Tapable {
     } catch (err) {
       throw new Error(`An error happened while parsing ${this._tsConfigPath} JSON: ${err}.`);
     }
+
+    if (options.hasOwnProperty('compilerOptions')) {
+      tsConfigJson.compilerOptions = Object.assign({},
+        tsConfigJson.compilerOptions,
+        options.compilerOptions
+      );
+    }
+
     const tsConfig = ts.parseJsonConfigFileContent(
       tsConfigJson, ts.sys, basePath, null, this._tsConfigPath);