Refactor source layout

Introduce compat source sets and move all kotlin sources to the main directory

[no changelog]

src/main/kotlin/events/EntityUpdateEvent.kt

@@ -0,0 +1,31 @@
+
+package moe.nea.firmament.events
+
+import net.minecraft.entity.Entity
+import net.minecraft.entity.LivingEntity
+import net.minecraft.entity.data.DataTracker
+import net.minecraft.network.packet.s2c.play.EntityAttributesS2CPacket
+
+/**
+ * This event is fired when some entity properties are updated.
+ * It is not fired for common changes like position, but is for less common ones,
+ * like health, tracked data, names, equipment. It is always fired
+ * *after* the values have been applied to the entity.
+ */
+sealed class EntityUpdateEvent : FirmamentEvent() {
+    companion object : FirmamentEventBus<EntityUpdateEvent>()
+
+    abstract val entity: Entity
+
+    data class AttributeUpdate(
+        override val entity: LivingEntity,
+        val attributes: List<EntityAttributesS2CPacket.Entry>,
+    ) : EntityUpdateEvent()
+
+    data class TrackedDataUpdate(
+        override val entity: Entity,
+        val trackedValues: List<DataTracker.SerializedEntry<*>>,
+    ) : EntityUpdateEvent()
+
+// TODO: onEntityPassengersSet, onEntityAttach?, onEntityEquipmentUpdate, onEntityStatusEffect
+}