Support multiple passes inside a Draw directive

[Gábor Gyebnár]

Introduce render passes inside a Draw block

// render_targets: [
// 	"color",
// 	"depth",
// ],
passes: [
	Pass(
		id: "shadow",
		depth_buffer: RenderTargetLevelZero("shadow-depth"),
	),
	Pass(
		id: "early_z",
		depth_buffer: RenderTargetLevelZero("depth"),
	),
	Pass(
		id: "solid",
		depth_buffer: RenderTargetLevelZero("depth"),
		color_buffers: [RenderTargetLevelZero("color")],
	),
],