Angular: Properly handle empty tsconfig compilerOptions

[matheo]

Issue:

What I did

Considered the case when tsconfig is extending another file and has an empty compilerOptions.

This avoid an exception like:

[gaetanmaisse]

I think we can merge this one but we need to plan some more work about the TS config, sum up of discussion I had with @ThibaudAV: we should follow the extends key to find the parent tsconfig.json and build the resulting one to be sure all the options/configs are taking into account.