Previously, some RxJS-related examples (which are not proper Angular apps) were not
tested on CI as part of the `example-e2e` npm script. This meant that the examples
could get out-of-date or contain compile errors without as noticing.
This commit ensures that the `example-e2e` script picks up these examples and checks
that they compile successfully.
Partly addresses #28017.
PR Close#34063
