Export all core APIs from `rxjs` module directly.

[benlesh]

Given the issue #6067 seems to be fairly difficult to solve, and given that we have renamed everything such that there are no conflicts between things like concat the creation function, and concat the operator, etc. Maybe it's time we talk about exporting all primary APIs from rxjs proper.

1. It's a non-breaking change.
2. It's the direction we've all discussed going many times.
3. It's easier to deal with, overall.

I'm talking about:

import { of, interval, take, concatWith, map } from 'rxjs';

interval(1000).pipe(
  take(3),
  concatWith(of('done')),
  map(x => `Tick: ${x}`)
)

[benlesh]

Oh, and to be clear, I'm not talking about rxjs/ajax, rxjs/fetch, rxjs/webSocket, or rxjs/testing. Overtime maybe those should be their own modules I'm not sure. For now, though, I wouldn't include them in this. I'm just talking about creation functions, subjects, operators, and schedulers.

[kolodny]

Isn't concat in both 'rxjs' and 'rxjs/operators'? Granted the operator is deprecated but will that be confusing to folks who assume everything is smooshed together?

[benlesh]

@kolodny we'd only move the newer name of the concat operator, which is concatWith.

[LayZeeDK]

Any notable effect on tree-shaking or overall TypeScript compilation speed?

[benlesh]

Core Team Meeting: General core team approval

• Doesn't need to be aligned with v7. Could be Minor release later.

[tmair]

Just as a side note. This change could also enable the use of API Extractor at least for the rxjs import location. The tool might help to automate detection of changes to the API surface of the library.