Compile Bevy game code to shared library instead of the engine itself

[Oracuda]

An issue with the current system

Bevy cannot be compiled to a shared library on windows due to the PE format, seemingly because gilrs produces multiple versions of WINAPI causing a very high number of external symbols being produced, exceeding the format's maximum of 65536.

A fix

Compile the game code as a shared library instead of the engine itself.

Why

This is the standard for most engines to compile or distribute the engine in a player format which automatically loads a shared library as the game code, or load the game code from the editor.

For example :

1. Godot's export templates with GDExtension
2. Unity's "Player" (Uses an embedded mono runtime for in-editor playback and in the player)
3. Unreal Engine's in editor hot-loading (?)

This could also possibly be a way to start the road to in-editor loading and playback.

Possible problem

The main entry point function would have to change to an exported function.