PiE: Play In Editor

Play in Editor (PiE) mode allows devs run the game directly in the engine's editor window without popping it out to another window allowing live previews of scene state via the normal level editor scene content tree and props panels.

The key here is to have PBGC and the core project compiler build a lib.rs file alongside the main.rs file. rather than creating a dedicated window this will export functions allowing GPU buffers and SceneDB refs to be shared between the game and the engine. this allows us to essentially compile and then "embed" the game directly in the engine on a temporary basis, pausing the built in Helio instance to save resources and perhaps even allow the same WGPU surface element to be used in the level editor to display in editor and in game frames