Support Setting a Size for Certain Sources

[grantjbutler]

Add a scaling mode for sources that can accept an arbitrary size (browser sources, color sources, and maybe other sources). With such a scaling mode, these sources can just set their size to the calculated size of the layout, rather than being set to a given size, like 1080x1920, and then scaled down to the calculated size.

For use cases like Twitch's Guest Star feature, this should mean that the nameplate of other users in the video call should be the right size and not scaled down and illegible. Additionally, I wonder if such a mode would then mean the render of various scenes would be more optimized? That is, I would assume (though I've not done much graphics programming) that rendering a source once at a desired size is more efficient than rendering it at a different size and then scaling to the desired size (but I don't know if this is actually the case, or if this is how OBS approaches scaling sources when rendering).