docs($sce): overhaul the `$sce` service documentation
docs($sce): overhaul the `$sce` service documentation

A big docs update around `$sce`:
There is a lot of content in there that is often misunderstood, and some of the
documentation starts to get really old too. Also fixed capitalization,
formatting, indentation and uniformized `@param` descriptions.

Closes #15735

Awingu/angular.js,Awingu/angular.js,Awingu/angular.js,Awingu/angular.js