Noncopyable generics (#2356)

* pitch v1

* fix typos; add more examples

* Fairly heavy edit: strip comments, break lines, remove 'inverse', remove dead sections

Future edits should be more incremental.

* Rework Motivation; other smaller edits

* Small wording nitpicks

* Remove inferred conditional copyability section

Still a few TODOs, but getting closer.

* Resolve remaining TODOs

Also:
* Diagnosing contradictory intent
* Rework ABI/API impact
* Alternative: Extension defaults
* Future: standard library and concurrency
* Future: tuples and packs

* Update proposals/NNNN-noncopyable-generics.md

* Updates

* more edits

* more edits

* more edits

* typos

* toc

* finishing touches

* Schedule non-copyable generics for review.

* Update file name for non copyable generics with SE number.

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Co-authored-by: Kavon Farvardin <[email protected]>
Co-authored-by: Tim Kientzle <[email protected]>
Co-authored-by: Holly Borla <[email protected]>

Author: 4 people