Add shader loading functionality

[no changelog]

src/main/kotlin/events/RegisterCustomShadersEvent.kt

@@ -0,0 +1,24 @@
+package moe.nea.firmament.events
+
+import com.mojang.datafixers.util.Pair
+import java.util.function.Consumer
+import net.minecraft.client.gl.ShaderProgram
+import net.minecraft.client.render.VertexFormat
+import net.minecraft.resource.ResourceFactory
+import moe.nea.firmament.Firmament
+
+data class RegisterCustomShadersEvent(
+    val list: MutableList<Pair<ShaderProgram, Consumer<ShaderProgram>>>,
+    val resourceFactory: ResourceFactory,
+) : FirmamentEvent() {
+    companion object : FirmamentEventBus<RegisterCustomShadersEvent>()
+
+    fun register(name: String, vertexFormat: VertexFormat, saver: Consumer<ShaderProgram>) {
+        require(name.startsWith("firmament_"))
+        try {
+            list.add(Pair.of(ShaderProgram(resourceFactory, name, vertexFormat), saver))
+        } catch (ex: Exception) {
+            Firmament.logger.fatal("Could not load firmament shader $name", ex)
+        }
+    }
+}