BLI: Inline math::min_max

For some reason this was not inlined. Considering it's a very simple function
and function call overhead could be measurable. In the case of the simple
brush benchmark file from the current sculpting project (#118145), this
improved performance by 6%, from 2.44s to 2.29s.

source/blender/blenlib/BLI_math_vector.hh

@@ -258,7 +258,7 @@ template<typename T, int Size>
 }
 
 template<typename T, int Size>
-void min_max(const VecBase<T, Size> &vector, VecBase<T, Size> &min, VecBase<T, Size> &max)
+inline void min_max(const VecBase<T, Size> &vector, VecBase<T, Size> &min, VecBase<T, Size> &max)
 {
   min = math::min(vector, min);
   max = math::max(vector, max);