Incremental presentation

[kvark]

Is your feature request related to a problem? Please describe.
Presenting full screen is wasteful if the user knows only a portion of the screen is changed.

Describe the solution you'd like
A native-only feature that allows the user to specify a rectangle to present.
This isn't a security concern, but a portability one.

Describe alternatives you've considered
No incremental present

Additional context
It's not clear if this is possible, given that the user of a swapchain doesn't know about the number of textures there. So there is no good way for the user to know the baseline, from which the changes were made.

[cwfitzgerald]

I highly suspect we will have to expose to the user the amount of images in the swapchain. It also implies letting people render to the swapchain without a clear, something that is currently disallowed.

[cwfitzgerald]

Closing in favor of #2869, this isn't as widespread as it seems.