feat(compiler): Added "strictMetadataEmit" option to ngc (#10951)

ngc can now validate metadata before emitting to verify it doesn't
contain an error symbol that will result in a runtime error if
it is used by the StaticReflector.

To enable this add the section,

  "angularCompilerOptions": {
    "strictMetadataEmit": true
  }

to the top level of the tsconfig.json file passed to ngc.

Enabled metadata validation for packages that are intended to be
used statically.

modules/@angular/forms/tsconfig-es2015.json

@@ -23,5 +23,8 @@
   "files": [
     "index.ts",
     "../../../node_modules/zone.js/dist/zone.js.d.ts"
-  ]
+  ],
+  "angularCompilerOptions": {
+    "strictMetadataEmit": true
+  }
 }

modules/@angular/forms/tsconfig-es5.json

@@ -24,5 +24,8 @@
   "files": [
     "index.ts",
     "../../../node_modules/zone.js/dist/zone.js.d.ts"
-  ]
+  ],
+  "angularCompilerOptions": {
+    "strictMetadataEmit": true
+  }
 }