fix(angular): expose executors sources (#8368)

* fix(angular): expose executors sources

when having custom builder relying on yours, explicit access to executors directory is now required with ng13. Otherwise calls such as `require("@nrwl/angular/src/executors/package/package.impl");` do not work anymore

* feat(angular): expose only executor functions

Co-authored-by: Colum Ferry <cferry09@gmail.com>

packages/angular/executors.ts

@@ -0,0 +1,3 @@
+export * from './src/executors/delegate-build/delegate-build.impl';
+export * from './src/executors/ng-packagr-lite/ng-packagr-lite.impl';
+export * from './src/executors/package/package.impl';

packages/angular/package.json

@@ -19,6 +19,7 @@
   ],
   "exports": {
     "./generators": "./generators.js",
+    "./executors": "./executors.js",
     "./tailwind": "./tailwind.js",
     "./src/generators/utils": "./src/generators/utils/index.js"
   },