[Observation] Proposal to add a transactional observation of values (#2726)

* Proposal to add a transactional observation of values

* Fix the placeholder SE#

* Update the interfaces to use `@isolated(any)` instead of `isolated` parameters

* Add a number of example cases to describe in more detail expected behaviors and potential edge cases

* Fix some spellings to the new behavioral section

* Transition to a non-optional construction and add a Iteration return version for explicitly constructing Observed untilFinished

* Observed is SE-0475

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Co-authored-by: Freddy Kellison-Linn <[email protected]>

Author: phausler