Introduce DefensiveMin and DefensiveMax

[ggwpez]

Add traits to run min/max operations defensively. In some cases we use min/max but do not expect the else case to trigger. These traits would help with finding if these cases actually ever trigger.

Was discussing it with Ank4n: can you add a defensive_min() and defensive_max as well? I think there are a LOT of use cases where we do these operations defensively.

Originally posted by @kianenigma in #12515 (comment)

trait DefensiveMin:

• fn defensive_min by using <=
• fn defensive_strict_min by using <

trait DefensiveMax:

• fn defensive_max by using >=
• fn defensive_strict_max by using >

[dharjeezy]

I want to pick this up @ggwpez
Can you give me an example of how this can be used like in this example [here] (https://github.com/paritytech/substrate/pull/12515/files#diff-a66e1f9bb70b6a5516c58534be76d45cf3339c5a56df4534ebfda632afb63bccR384) ?

[ggwpez]

Example being something like:

assert_eq!(10, 10_u32.defensive_min(11_u32)); // works
assert_eq!(10, 11_u32.defensive_min(10_u32)); // panics in tests

That is at-least how I imagine it. Should be possible in Rust hopefully. @dharjeezy