Fabric module refactor

[booky10]

Breaking changes

• The PacketEvents instance now needs to be created using either PacketEventsServerMod#constructApi(String) or PacketEventsClientMod#constructApi(String)
• Nearly all packetevents fabric internals have been changed

Changes

• Splits sources into client and common sources to prevent accidentally using client code
• Sets up a PacketEvents api instance on both the client and server
• Simplifies network pipeline injection and encoder/decoder handling
• Uses proper SLF4J logger instead of System.out
• Uses fabric access wideners for accessing player connection internals instead of reflection
• Fixes https://github.com/retrooper/packetevents/issues/1025

Todo

• [x] Look at other platforms and search for stuff which could be missing
  • [x] Associate platform player instance with connection channel
• [x] Testing on client and dedicated server
• [ ] ~~Find a way to create packetevents instances for singleplayer worlds (internal server; maybe using events other mods could listen to?)~~
  • Not possible without loading packetevents on an additional, separate classpath or removing usage of the static instance (which is used everywhere...)