USDZExporter: Fix Object indentation level

[mkeblx]

Description

Add 3 tabs for Object_x's as they should always be placed at 3 levels in with the current exporter fixed output structure.

Before:

def Xform "Root"
{
	def Scope "Scenes" (
		kind = "sceneLibrary"
	)
	{
		def Xform "Scene" (
			customData = {
				bool preliminary_collidesWithEnvironment = 0
				string sceneName = "Scene"
			}
			sceneName = "Scene"
		)
		{
def Xform "Object_15" (
	prepend references = @./geometries/Geometry_3.usda@</Geometry>
	prepend apiSchemas = ["MaterialBindingAPI"]
)
{
	matrix4d xformOp:transform = ( (1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (0, 0, 0, 1) )
	uniform token[] xformOpOrder = ["xformOp:transform"]

	rel material:binding = </Materials/Material_6>
}
...

After:

def Xform "Root"
{
	def Scope "Scenes" (
		kind = "sceneLibrary"
	)
	{
		def Xform "Scene" (
			customData = {
				bool preliminary_collidesWithEnvironment = 0
				string sceneName = "Scene"
			}
			sceneName = "Scene"
		)
		{
			def Xform "Object_15" (
				prepend references = @./geometries/Geometry_3.usda@</Geometry>
				prepend apiSchemas = ["MaterialBindingAPI"]
			)
			{
				matrix4d xformOp:transform = ( (1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (0, 0, 0, 1) )
				uniform token[] xformOpOrder = ["xformOp:transform"]

				rel material:binding = </Materials/Material_6>
			}
...