Implement playable Mac client and rendering validation

test/rendering/particle-leak/main.gd

@@ -0,0 +1,17 @@
+extends Node
+var refs: Array[WeakRef] = []
+func _ready() -> void: call_deferred("run")
+func run() -> void:
+	for i in 8: create_material(i)
+	for i in 10: await get_tree().process_frame
+	RenderingServer.force_sync()
+	var alive := 0
+	for reference in refs:
+		if reference.get_ref() != null: alive += 1
+	print("ISOLATED_PARTICLE_EXIT alive=", alive)
+	get_tree().quit(1 if alive else 0)
+func create_material(index: int) -> void:
+	var material := ParticleProcessMaterial.new()
+	material.emission_shape = index % 3
+	material.get_rid()
+	refs.append(weakref(material))