Texenvs need to be dirtied if changed mid frame

When mid-frame (inside `Instance::render_with`),
if you have some sort of
```rust
loop {
  setup_texenvs(&mut instance);
  instance.draw(whatever);
}
```
you need to dirty the texenvs before they are changed (I put the texenv dirtying at the end of the loop when implementing `egui` on the 3DS)