VoxelManip cleanups (const ref, const move) + function removal (#6169)

VoxelManip cleanups (const ref, const move) + function removal (#6169)

* VoxelManip cleanups (const ref, const move) permitting to improve a little bit performance

* VoxelArea: precalculate extent (performance enhancement)

This permits to reduce extend high cost to zero and drop many v3s16 object creation/removal to calculate extent
It rebalance the client thread update to updateFastFaceRow instead of MapBlockMesh generation
This will also benefits to mapgen