Nether portal teleportation is inaccurate at large coordinate values

In PortalShape::getRelativePosition an unnecessary conversion from double to float leads to excessive rounding of the position you end up when going through a portal.

Reproduction steps:

• Open the attached world
• Click the minecart to position the player at 8000000.5 8000000.5
• You get teleported to 1000000.5 1000000.348 instead of 1000000.5 1000000.5