[feature request] prefer-rxjs replace rxjs/operators with rxjs

[JounQin]

See ReactiveX/rxjs#6488

[cartant]

A rule that flags imports from "rxjs/operators" as failures would be very easy, but writing fixers for rules is somewhat tedious. I'll probably add this eventually, but it's not near the top of my list of things to do.

Actually, even a rule without a fixer is fairly complicated, as there are a handful of deprecated operators still need to be imported from "rxjs/operators".

[JounQin]

I finish up by using core rule no-restricted-imports

{
  "rules": {
    "no-restricted-imports": [
      2,
      {
        "paths": [
          {
            "name": "rxjs/operators",
            "message": "Please use top level `rxjs` directly instead."
          }
        ]
      }
    ]
  }
}