`main()` function used to be needed to support dart, since dart
Does not allow top level statements. Since we no longer use dart
The need for `main()` has been removed.
In preparation for `Basel` and standardized way of running tests
we are removing `main()`
PR Close#21053
This is required as e.g. `token` from `@Inject` is
accessed in string form via makeParamDecorator
but as a property in the `ReflectiveInjector`.
Closes#16889 as this is a more general fix.