Refactor source layout

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

[no changelog]

src/main/kotlin/events/EarlyResourceReloadEvent.kt

@@ -0,0 +1,10 @@
+
+package moe.nea.firmament.events
+
+import java.util.concurrent.Executor
+import net.minecraft.resource.ResourceManager
+
+data class EarlyResourceReloadEvent(val resourceManager: ResourceManager, val preparationExecutor: Executor) :
+    FirmamentEvent() {
+    companion object : FirmamentEventBus<EarlyResourceReloadEvent>()
+}