Rewritten proposal for Windowing 3.0 + Input 3.0 updates (#2353)

* New windowing proposal

* Out of date anaology

* Some fixes from putting it in an IDE

* Add IDetachedSurfaceLifecycle

* Add a windowed fullscreen setting on request of Stride

* Minor proposal updates

* Add ScaleChanged event, some improvements

* Modify Mutli-Backend Input

* Fixes from comments i think

* Update proposal to add 'virtual pointers'

* Remove half-baked virtual pointers API

* Updates from WG review

* Input updates from WG review

* Credits

Author: Perksey