Prevent static initialization order fiasco for all class constants

[scpeters]

There is a possibility of static initialization order fiasco when the order in which objects with static storage duration are initialized is ambiguous (see example code to reproduce the problem). Several classes were updated recently to use constexpr for initializing static constants, and these fixes should be applied to other class constants as well:

• Use safe idiom for math constants. #2231
• Use constexpr for static colour constants #3313
• Use constexpr for static Vector constants #3315
• AxisAlignedBox
• OgreMatrix3
• OgreMatrix4
• OgreAffine
• OgreQuaternion
• add others