Disable layer hoisting for non-8888 canvases

This just stops the bleeding. A real fix would propagate the canvas' backing type down to the layer hoister.

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1957433002

Review-Url: https://codereview.chromium.org/1957433002
2 files changed