Off-center rotation with Circle and RoundRect.

New project, Korge 2.3.3 with below code:

```kotlin
suspend fun main() = Korge(virtualWidth = 640, virtualHeight = 400, bgcolor = Colors.WHITE) {
val test = circle(radius = 20.0, fill = Colors.BLACK) {
position(320.0, 200.0)
anchor(0.5, 0.5)
}

test.addUpdater { dt ->
test.rotation(test.rotation + 120.degrees * dt.seconds)
}
}
```

Calling ```anchor(0.5, 0.5)``` should place the transform origin to view's center, right? Yet resulting motion is off-center. Furthermore, the wobble radius increases with the window size. The problem also appears when same transformation applied to a RoundRect, but doesn't when SolidRect or Image is used.

Edit: I think this is the same issue with #379.

Reproduce the issue with the provided Kotlin example, then compare rotation and anchoring for Circle and RoundRect against SolidRect and Image. Start by tracing the anchor and rotation behavior used by these shapes; done means Circle and RoundRect rotate around their centered anchors without window-size-dependent wobble.

Written by the indexing model from the issue text.