This patch implements the vector types (i.e:float2) by making heavy
usage of templating. All vector functions are now outside of the vector
classes (inside the blender::math namespace) and are not vector size
dependent for the most part.

In the ongoing effort to make shaders less GL centric, we are aiming
to share more code between GLSL and C++ to avoid code duplication.

Motivations:

• We are aiming to share UBO and SSBO structures between GLSL and C++. This means we will use many of the existing vector types and others we currently don't have (uintX, intX). All these variations were asking for many more code duplication.
• Deduplicate existing code which is duplicated for each vector size.
• We also want to share small functions. Which means that vector functions should be static and not in the class namespace.
• Reduce friction to use these types in new projects due to their incompleteness.
• The current state of the BLI_(float|double|mpq)(2|3|4).hh is a bit of a let down. Most clases are incomplete, out of sync with each others with different codestyles, and some functions that should be static are not (i.e: float3::reflect()).

Upsides:

• Still support .x, .y, .z, .w for readability.
• Compact, readable and easilly extendable.
• All of the vector functions are available for all the vectors types and can be restricted to certain types. Also template specialization let us define exception for special class (like mpq).
• With optimization ON, the compiler unroll the loops and performance is the same.

Downsides:

• Might impact debugability. Though I would arge that the bugs are rarelly caused by the vector class itself (since the operations are quite trivial) but by the type conversions.
• Might impact compile time. I did not saw a significant impact since the usage is not really widespread.
• Functions needs to be rewritten to support arbitrary vector length. For instance, one can't call len_squared_v3v3 in math::length_squared() and call it a day.
• Type cast does not work with the template version of the math:: vector functions. Meaning you need to manually cast float * and (float *)[3] to float3 for the function calls. i.e: math::distance_squared(float3(nearest.co), positions[i]);
• Some parts might loose in readability: float3::dot(v1.normalized(), v2.normalized()) becoming math::dot(math::normalize(v1), math::normalize(v2)) But I propose, when appropriate, to use using namespace blender::math; on function local or file scope to increase readability. dot(normalize(v1), normalize(v2))

Consideration:

• Include back .length() method. It is quite handy and is more C++ oriented.
• I considered the GLM library as a candidate for replacement. It felt like too much for what we need and would be difficult to extend / modify to our needs.
• I used Macros to reduce code in operators declaration and potential copy paste bugs. This could reduce debugability and could be reverted.
• This touches delaunay_2d.cc and the intersection code. I would like to know @Howard Trickey (howardt) opinion on the matter.
• The noexcept on the copy constructor of mpq(2|3) is being removed. But according to @Jacques Lucke (JacquesLucke) it is not a real problem for now.

I would like to give a huge thanks to @Jacques Lucke (JacquesLucke) who helped during this
and pushed me to reduce the duplication further.