This commit updates the docs examples to be compatible with the
`prefer-const` tslint rule.
This is in preparation of updating the docs examples `tslint.json` to
match the one generated for new Angular CLI apps in a future commit.
PR Close#38143
Previously, the examples in the `comparing-observables` guide were hard-coded.
This made it impossible to test them and verify they are correct.
This commit fixes this by converting them into a proper mini-app. In a
subsequent commit, tests will be added to verify that the source code
works as expected (and guard against regressions).
Fixes#31024
PR Close#34327
George Kalpakas
Sonu Kapoor
thanhpd
Suguru Inatomi
thanhpd
Ro Savage
Anuj
SangKa.Z
Jason Aden