FillConstraint: Fix positioning not being accounted for

[Sychic]

Previously did not account for the component's position within the parent, resulting in larger than expected sizing.

[Johni0702]

This cannot be merged because:

1. It changes existing behavior of FillConstraint (this is after all the point, but it will break code that has come to rely on the old behavior)
2. It causes a cyclic constraints error if the component on which the FillConstraint is applied has a position constraint that directly or indirectly depends on its size
3. It causes a cyclic constraints error if any sibling component has a position constraint that directly or indirectly depends on the size of the component
4. It only accounts for padding on components on the left (those where that padding is being accounted for by the x position of the components) but not for any padding on components on the right. (granted, it didn't set out to do that, but it only working properly when left-aligned and breaking when right-aligned is certainly not great)