build: Use multi-version and preprocessor to build all target versions from one branch (#463)

* feat: convert Fabric to use essential-multi-version

* fix: populate compatibility.yml with mc version

* feat: start WIP work on doing the same for bukkit

* refactor: use preprocessor plugin to multi-version bukkit

* docs: update README to mention multi-version stuff

* build: also include javadocs for Bukkit

* build: update CI workflows

also slightly simplifies buildscript

gradle.properties

@@ -3,13 +3,12 @@ org.gradle.jvmargs='-Dfile.encoding=UTF-8'
 org.gradle.daemon=true
 javaVersion=21
 
-# Plugin settings
+# Plugin metadata
 plugin_version=3.7.3
-minecraft_version=1.21.4
 plugin_archive=husksync
 plugin_description=A modern, cross-server player data synchronization system
 
-# Drivers
+# General settings
 jedis_version=5.2.0
 mysql_driver_version=9.2.0
 mariadb_driver_version=3.5.1
@@ -17,15 +16,5 @@ postgres_driver_version=42.7.5
 mongodb_driver_version=5.3.1
 snappy_version=1.1.10.7
 
-# Spigot/Paper build settings
-bukkit_spigot_api=1.21.4-R0.1-SNAPSHOT
-bukkit_paper_api=1.21.4-R0.1-SNAPSHOT
-
-# Fabric build settings
-fabric_loom_version=1.9-SNAPSHOT
-fabric_loader_version=0.16.10
-fabric_yarn_mappings=1.21.4+build.8
-fabric_api_version=0.115.0+1.21.4
-fabric_adventure_platform_version=6.2.0
-fabric_permissions_api_version=0.3.3
-fabric_sgui_version=1.8.2+1.21.4
+# Fabric settings
+fabric_loom_version=1.9-SNAPSHOT