* feat(common): support `as` syntax in template/* bindings
Closes#15020
Showing the new and the equivalent old syntax.
- `*ngIf="exp as var1”`
=> `*ngIf="exp; let var1 = ngIf”`
- `*ngFor="var item of itemsStream |async as items”`
=> `*ngFor="var item of itemsStream |async; let items = ngForOf”`
* feat(common): convert ngIf to use `*ngIf="exp as local“` syntax
* feat(common): convert ngForOf to use `*ngFor=“let i of exp as local“` syntax
* feat(common): expose NgForOfContext and NgIfContext
