Previously, the generated StackBlitz examples as well as the
corresponding downloadable zips for the `http` guide examples were not
correct and thus trying to run the app and/or tests would fail.
This commit fixes the examples:
- Replace `TestBed.inject()` (which was [introduced in v9][1]) with
`TestBed.get()` (which is available in v8 used in the examples).
(NOTE: The examples will soon be updated to v9 (as part of
[FW-1609][2] and switched back to `TestBed.inject()` then.)
- Include `src/app/heroes/hero.ts` in the zip, because it is referenced
by some of the other files and the compilation fails without it.
- Ensure `src/main-specs.ts` is not included in the zip that does not
include the tests. Including the file broke the app, because there is
logic in our zip-builder that renamed `main-*.ts` files to `main.ts`
and thus `main-specs.ts` ended up overwriting the actual `main.ts`.
[1]: https://next.angular.io/guide/deprecations#angularcoretesting
[2]: https://angular-team.atlassian.net/browse/FW-1609Fixes#33874Fixes#33945
PR Close#33941