take and borrow parameter ownership modifiers (#1739)

* Michael's working draft from https://github.com/gottesmm/swift-evolution/blob/consuming-nonconsuming-pitch-v1/proposals/000b-consuming-nonconsuming.md

* New revision based on feedback from SE-0366

* Revisions in response to pitch discussion:

- Use `taking` and `borrowing func` modifiers to control `self`'s convention
- Add "alternative considered" for whether `take`n parameters should be bound
  as mutable in the callee

* More additions from pitch discussion

- Mention that nonescaping closure arguments cannot be `take`-n
- Mention "out" parameter conventions as a future direction
- Include discussion of destructuring move-only values that normally would have destructors,
  without invoking the normal deinit

* Remove "future direction" of destructuring methods

This fits better thematically as a future direction discussion with the `take` operator
proposal instead.

* Based on initial WG guidance, start off with suggesting that takes are locally mutable

* Clarify how witness matching works with move-only parameters: the ownership must match exactly

* Update and rename NNNN-parameter-ownership-modifiers.md to 0377-parameter-ownership-modifiers.md

Co-authored-by: Ben Cohen <[email protected]>

Author: jckarter