Update three d (#1793)

* Update three-d to 0.12

* Fix Z fighting in three-d example

Closes https://github.com/emilk/egui/issues/1744

* cargo deny: ignore three-d (only used in examples)

deny.toml

@@ -37,6 +37,7 @@ skip = [
 skip-tree = [
     { name = "criterion" }, # dev-dependnecy
     { name = "glium" },     # legacy crate, lots of old dependencies
+    { name = "three-d" },   # example dependency
 ]