Add begin,end support for glm

[ZXShady]

This pr adds glm::begin,glm::end,glm::rbegin,glm::rend to allow for usage with iterators and importantly ranged based for loop.

This function is overloaded for vec,mat,qua types.

Example uses of this pr

int total = 0;
for(auto& elem : vec) {
   total += elem;
}

// find elem
auto it = std::find(begin(vec),end(vec),21);

This differs from PR #1327 because it overloads the functions with specilized templated types and not just a template parameter therefore it allows proper ADL. and also it adds rbegin and rend

[AbitTheGray]

I would still argue for using "gtc/type_trait.hpp" (as I did in #1327 ), or something similar, instead of different values you've used in end (I especially don't like the 4 there, even tho it will never change).

[ZXShady]

I would still argue for using "gtc/type_trait.hpp" (as I did in #1327 ), or something similar, instead of different values you've used in end (I especially don't like the 4 there, even tho it will never change).

why? it just seems unnecessary when I can just calculate it inline since I already need to explicitly specify the template class for ADL to work. I didn't even want to provide it for qua but it would seem inconsistent so I hesitated to remove it

@AbitTheGray

[ZXShady]

Fixed the #ifdef

[christophe-lunarg]

Thanks for contributing!

[ZXShady]

Thanks for accepting my pull request 🙂