Use sky API to obtain directional light source position

[x2048]

Refactor calculation of sun/moon position to be in the Sky class, so that it is easy to use in e.g. shaders.
Fixes a bug where sun position on the sky and shadow direction are not aligned with high values of sky_body_orbit_tilt

To do

This PR is Ready for Review.

How to test

Test1

1. Set sky_body_orbit_tilt = 30
2. Enable dynamic shadows
3. Start a game
4. Set time to 10:00
5. Align player's shadow with an object in the world (e.g. tree trunk or a stack a nodes).
6. Look at the sun and check that the light source is behind the object.
7. Perform the same test with moon at 22:00

Test2

1. Set sky_body_orbit_tilt = 30
2. Start a game (MTG)
3. Set time to 6:00
4. Look at the sun, the texture must not be rotated