This changes the public api spec to check each public barrel individually
to make sure its API has not changed. The previous API spec has been
preserved but split into respective barrels.
The compiler barrel has been added to the spec, along with all of its
public exports. Previously, angular2/angular2 was only exporting a
handful of symbols from compiler, so there are now many more symbols
being tested in the spec for compiler than previously.
Part of #5710Closes#5841
Supercedes #5821
Jeff Cross
Tim Blasi
vsavkin
Misko Hevery