"ng update" supports having multiple packages as part of a group which should be updated together, meaning that e.g. calling "ng update @angular/core" would be equivalent to updating all packages of the group (that are part of the package.json already).
In order to support the grouping feature, the package.json of the version the user is updating to needs to include an "ng-update" key that points to this metadata.
The entire specification for the update workflow can be found here: 2e8b12a4ef/docs/specifications/update.md
PR Close#22482
* Remove now unnecessary portions of build.
* Add a compilePackageES5 method to build ES5 from sources
* Rework all package.json and rollup config files to new format
* Remove "extends" from tsconfig-build.json files and fixup compilation roots
PR Close#18541
Hans Larsen
Jason Aden
Chuck Jazdzewski
Jason Aden