Make @fortawesome/fontawesome-svg-core a regular dependency

[devoto13]

The main reason why it was a peer dependency is because it contained a global library variable. Therefore it was important to ensure that there is only one instance of library. Furthermore consumers had to import library from @fortawesome/fontawesome-svg-core, so they often installed it as a directly dependency. This result in two instances and lots of troubles.

angular-fontawesome provides its own FaIconLibrary now and support for icon library from fontawesome-svg-core will be removed in 0.7.0. It is a long standing goal to make fontawesome-svg-core an implementation detail of angular-fontawesome, so consumers don't need to worry about its existence.

To achieve this several things needs to be done:

• move @fortawesome/fontawesome-svg-core to regular dependencies
• ensure that all types from @fortawesome/fontawesome-svg-core used by angular-fontawesome are re-exported
• provide ng update command, which will remove @fortawesome/fontawesome-svg-core from user's package JSON not trivial, so the migration will require a manual step
• resolve dom.watch() causes a lot of problems in Angular 8 #171 by writing a guide, so people using dom.watch() with Angular know how to achieve it