Add ensure, and ensureNotNull in computation DSL

[nomisRev]

This PR adds some convenient syntax for mixing the nullable effect/monad with other effect/monads such as either, option and nullable itself.

It also deprecates the currently gotcha behavior of nullable bind syntax in option { }.
Example of gotcha behavior:

either<Int, String> {
  option<Int> {
     Either.Left(1).bind() // Expected to short-circuit but uses `fun <A> A?.bind(): A` instead and *doesnt* short-circuit,
     
  }.fold({ "0" }, Int::toString)
}

This was originally proposed in #2311.
The proposed require/requireNotNull syntax conflicts with with kotlin.require and kotlin.requireNotNull which is auto-imported and it can be easily confused. If it's mistake it leads to an exception instead of participating in the computation block.

[franciscodr]

Task linked: CU-p9935d Add special validation syntax like kotlin.require and kotlin.requireNotNull

[nomisRev]

Closes #2311

[raulraja]

Looks great @nomisRev !

[i-walker]

🙌🏾 Thanks Simon