Abstract out creation "Of" and conversion "To" Quantity members

[atmoos]

• All quantities had "Copy Paste" versions of To{...} and Create{...} methods.
• Now replaced by reusable structs
• Held together by IFactory<TQuantity, TDimension> interface
• Performance has degraded, but
• Readability has increased (this has higher importance)

Note: Naming is still bad in many (new) areas. Ought to change when I publish this PR.

Initially borne out of an idea to make serialization easier...

In a nutshell

Previously:

Length smallMetric = Length.Si<Micro, Metre>(23);

Now:

Length smallMetric = Length.Of(23).Si<Micro, Metre>();

[sereneowl]

Most questions are questions about understanding what you did. Stuff like:

• when do you use Create and when an internal constructor
• when do you use struct and when class
• why do some quants have a root while others don't.

I hope that the next reviews will be smaller because I wish to dive deep in understanding what you actually built here 😁