ngfactory files have a ɵNonEmptyModule constant included if there are no
other exported factory symbols. Previously this extra export was added
dynamically in a TS transformer.
However, synthetically constructed exports don't get properly downleveled
during JS emit, and this generated constant caused issues with downstream
tests.
Instead, this commit configures the shim to always have this export to
begin with, and to filter it out if it's not required.
Testing strategy: covered by existing ngtsc_spec tests which verify the
presence of the ɵNonEmptyModule symbol.
PR Close#27483
276bdd1f3e