Analogously to directives, the `ngInjectableDef` field in .d.ts files is
annotated with the type of service that it represents. If the service
contains required generic type arguments, these must be included in
the .d.ts file.
PR Close#27037
Previously the concept of multiple directives with the same selector was
not supported by ngtsc. This is due to the treatment of directives for a
component as a Map from selector to the directive, which is an erroneous
representation.
Now the directives for a component are stored as an array which supports
multiple directives with the same selector.
Testing strategy: a new ngtsc_spec test asserts that multiple directives
with the same selector are matched on an element.
PR Close#27298
