CALayer: Set the default contentsScale to screen scale, update to match contents

[Adlai-Holler]

Currently we hack this into ASImageNode but really it applies to any node.

Without this, if you're on a 2.0 screen and you set the content mode of a text to, say, TopLeft, the text will be twice its size i.e. rendered at 1.0, and you can only see the top left quarter of the contents.

Basically, we are currently relying on UIViewContentModeScaleToFill/kCAGravityResize (the default) to apply our contentsScale. This is wrong and bad.

UIView sets contents scale based on the screen, we should do the same thing on our own.

• Change the default to main screen scale.
• When a contents image is applied to the layer, match its contentsScale to the contents image.
  • Old behavior was to set the node's contentsScale to the layer's contentScale but this is nonsensical, since the node's contentsScale is a bridged property from the layer! It was a no-op.

This is by no means the perfect state (we will still trample on a user-set value of contentsScale, but that's insanely rare) but it's better, and it's similar to how UIKit handles this.

[nguyenhuy]

@Adlai-Holler Can you rebase with master to unblock the CI?

[Adlai-Holler]

Sure, done

[ghost]

🚫 CI failed with log

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