Add helper functions to create AxisAlignedBox objects from other shapes

[scpeters]

Desired behavior

Add helper functions that create an AxisAlignedBox object when passed a shape object like Box, Capsule, Cylinder, etc.

Alternatives considered

Implementation suggestion

Add static helper functions to a separate header file (such as include/gz/math/AxisAlignedBoxHelpers.hh) with the following API:

static gz::math::AxisAlignedBox ConvertToAxisAlignedBox(const gz::math::Box &);
static gz::math::AxisAlignedBox ConvertToAxisAlignedBox(const gz::math::Sphere &);
static gz::math::AxisAlignedBox ConvertToAxisAlignedBox(const gz::math::Capsule &);
etc.

Additional context

This was motivated by the feature proposed by @gabrielfpacheco in gazebosim/sdformat#1547.

[anshium]

I have implemented the functions for Box, Sphere, Capsule and Cylinder. They seem to work. Also wrote test cases to check the correctness and all of them pass.

Codecheck has problems with length of lines and whitespaces. I will make a PR, once I fix those things.

I, however, have a few doubts:

1. Do I update the Python Bindings?
2. Do I write an example?
3. Where do I update the documentation?