G3 is now using RXJS version 7 which makes it possible for the CLI to also be updated to RXJS 7.
NB: this change does not remove all usages of the deprecated APIs.
Closes#24371
This should clean up the code a bit.
Note: at first I added the no-useless-cast rule, but after getting frustrated
with it (as it has many false positive), I decided to remove the rule but some
useless casts were removed so I let those in the PR.