Add shape-content budget to bound repeater cost

Repeaters can multiply a shape by up to 10000 copies, and each shape
can have up to 1024 points. Multiplying both together (or nesting
repeaters inside each other) could still produce very large amounts
of render work per frame, even though each setting on its own stayed
within the existing limits.

Add a shared budget (15000 weighted points) that is spent while
building the shape tree. Point-heavy shapes (stars, custom paths)
spend more of the budget, simple shapes spend very little. Repeater
copies and nested repeaters draw from the same shared budget, so
copies stop being created once it runs out.

Patch keeps normal animations working as before, while capping the
worst-case render cost for unusual or extreme content.