Replace a built-in overlay

Swap out a built-in overlay for a custom implementation.

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Every canvas overlay — the selection brush, scribble, snap indicators, shape handles — is an OverlayUtil subclass you can replace. This example extends the built-in BrushOverlayUtil and overrides its render method to draw a dashed purple rectangle in place of the default gray one. Drag-select on the canvas to see it.