feature suggestion: constexpr vector operators

[ribbon-otter]

It would be nice to be able to do Ogre::Vector3 math in a constexpr context, like

    constexpr Vector3 half_map_size = map_size / 2;

For my set up (c++23 and gcc), the following already works.

   constexpr Vector3 map_size = Vector3(10,10,10); 

I would be interested in trying my hand at this, but I thought I suggest it first to measure interest; particularly for which C++ versions we need to support since the constexpr rules vary significantly by C++ version.

[paroj]

for ogre 14, we target c++14, for ogre 15 we might move up to c++17. You could also guard the constexpr with macros, as so it still works in c++17 user code.

Generally, I dont see why we should not improve constexpr support.