Improve Mod Loading

[TYKUHN2]

Improve mod loading to improve startup performance of Forge. Early tests show Forge substantially slows startup, even without mods third party mods.

Potential improvements include a better framework, use of newer APIs, or multithreaded loading. Ideally, mods compiled for upstream should still be supported, so ABI must be maintained.

[TYKUHN2]

Asynchronous mod loading appears to be working in the asynchronous branch, but further testing needs to be done to evaluate effectiveness.