This allows us to avoid many calls to `as_span()` methods. I will
remove those in the next commit. Furthermore, constructors
of Vector and Array can convert from one type to another now.
I tested these changes on Linux with gcc and on Windows.
Even if we do not use exception in many places in Blender, our core C++ library
should become exception safe. Otherwise, we don't even have the option
to work with exceptions if we decide to do so.
The main focus here was to improve the docs significantly. Furthermore,
I reimplemented `Set`, `Map` and `VectorSet`. They are now (usually)
faster, simpler and more customizable. I also rewrote `Stack` to make
it more efficient by avoiding unnecessary copies.
Thanks to everyone who helped with constructive feedback.
Approved by brecht and sybren.
Differential Revision: https://developer.blender.org/D7931