FLIP 357: Add Comparison Functions to Cadence

[turbolent]

Work towards #357

[SupunS]

+1

[bluesign]

yeah this is much needed. I love it. ( I would also love clamp(value, min, max) )

[joshuahannan]

this will be great to have!

[turbolent]

I've updated the proposal in a8a2a4d:

• Renamed the functions to min/max, so they have familiar names, like in most other languages
• Define the functions in the new contract Comparison, instead globally. This avoids any naming conflicts and guarantees backward compatibility for existing code

[turbolent]

Added a clamp function in c05e5f4. cc @bluesign