Initial 1.16.5/Sponge API 8 Functionality (Currently Forge Only)

[NickImpact]

This provides initial 1.16.5/Sponge API 8 compatibility. There are likely some packet mappings to adjust, as well as additional improvements that can be made to the API (such as custom packet type definitions).

At present, this code is only capable of running on Forge. Between SV and SF, there is some mapping incompatibility that will require some additional research to get working with both platforms. Due to environment issues, this was not tremendously tested, and was only verified for bootup success. Ideally, this should move away from ForgeGradle and instead use VanillaGradle, but perhaps there's an additional method we can use to have ForgeGradle mappings work with SV.

Notable differences:

• Upgraded Gradle to 7.3.3, FG to 5.1+ and SG 2.0.1
• Reverted indigo to base kyori distribution due to repository resolution issues
• To my knowledge, Sponge removed custom services on the service provider, so added a new ServiceProvider class responsible for providing the service.
• Updated access privileges where it made sense (IJ loved to complain about this)
• Removed reliance on SpongeCommon