feat: add MergeEventQueues node

Concatenates two event queues into one, enabling multiple event sources
to feed into a single event queue input (e.g. FSM driver).

Author: baszalmstra

crates/bevy_animation_graph_builtin_nodes/src/event_queue/merge_event_queues.rs

@@ -0,0 +1,43 @@
+use bevy::prelude::*;
+use bevy_animation_graph_core::{
+    animation_node::{NodeLike, ReflectNodeLike},
+    context::{new_context::NodeContext, spec_context::SpecContext},
+    edge_data::DataSpec,
+    errors::GraphError,
+};
+
+/// Merges two event queues into one.
+#[derive(Reflect, Clone, Debug, Default)]
+#[reflect(Default, NodeLike)]
+#[type_path = "bevy_animation_graph::builtin_nodes"]
+pub struct MergeEventQueues;
+
+impl MergeEventQueues {
+    pub const IN_A: &'static str = "in_a";
+    pub const IN_B: &'static str = "in_b";
+    pub const OUTPUT: &'static str = "out";
+
+    pub fn new() -> Self {
+        Self
+    }
+}
+
+impl NodeLike for MergeEventQueues {
+    fn display_name(&self) -> String {
+        "Merge Events".into()
+    }
+
+    fn update(&self, mut ctx: NodeContext) -> Result<(), GraphError> {
+        let a = ctx.data_back(Self::IN_A)?.into_event_queue()?;
+        let b = ctx.data_back(Self::IN_B)?.into_event_queue()?;
+        ctx.set_data_fwd(Self::OUTPUT, a.concat(b));
+        Ok(())
+    }
+
+    fn spec(&self, mut ctx: SpecContext) -> Result<(), GraphError> {
+        ctx.add_input_data(Self::IN_A, DataSpec::EventQueue)
+            .add_input_data(Self::IN_B, DataSpec::EventQueue)
+            .add_output_data(Self::OUTPUT, DataSpec::EventQueue);
+        Ok(())
+    }
+}

crates/bevy_animation_graph_builtin_nodes/src/event_queue/mod.rs

@@ -1,2 +1,3 @@
 pub mod fire_event;
 pub mod map_events;
+pub mod merge_event_queues;

release-content/release-notes/merge_event_queues.md

@@ -0,0 +1,7 @@
+---
+title: Merge Event Queues Node
+authors: ["@baszalmstra"]
+pull_requests: []
+---
+
+A new `MergeEventQueues` node has been added that concatenates two event queues into one. This is useful when multiple event sources (e.g. a `FireEventNode` and a `ClipNode`'s event output) need to feed into a single event queue input like the FSM's driver.