Refactor source layout

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

[no changelog]

src/main/kotlin/events/BakeExtraModelsEvent.kt

@@ -0,0 +1,21 @@
+
+package moe.nea.firmament.events
+
+import java.util.function.Consumer
+import net.minecraft.client.util.ModelIdentifier
+
+class BakeExtraModelsEvent(
+    private val addItemModel: Consumer<ModelIdentifier>,
+    private val addAnyModel: Consumer<ModelIdentifier>,
+) : FirmamentEvent() {
+
+    fun addNonItemModel(modelIdentifier: ModelIdentifier) {
+        this.addAnyModel.accept(modelIdentifier)
+    }
+
+    fun addItemModel(modelIdentifier: ModelIdentifier) {
+        this.addItemModel.accept(modelIdentifier)
+    }
+
+    companion object : FirmamentEventBus<BakeExtraModelsEvent>()
+}