Add support for Web Test Runner in @nx/angular:library

[FrancescoBorzi]

Currently, the only supported unitTestRunner for [@nx/angular:library}(https://nx.dev/nx-api/angular/generators/library) is jest. I understand karma has been deprecated and is no longer available in NX.

Since Angular announced its transition to Web Test Runner (see this announcement from the Angular Blog) it would be nice to add it to NX as well.

This would be particularly useful since at the moment the combo Angular+Jest has a serious performance issue ( see thymikee/jest-preset-angular#2161 ) and unit tests run quite slow.

[gperdomor]

Not only for angular libraries, I think should be supported by @nx/js:library too...