Simplify Range<T> usage and implementation, switching to half-open (end is exclusive)

[YoshiRulz]

WIP, but the next part will be much harder, so if you want to review and merge don't wait for me do not merge without unit tests.

After merge, need to remember to update https://github.com/TASEmulators/BizHawk/wiki/Available-C%23-and-.NET-features

[Morilli]

What's the WIP part about this? Could this just be merged as is or is something missing?

[YoshiRulz]

It could be merged as-is. (It might be a good idea to have a unit test, at least before the refactor from closed to half-open, since that one changes some logic.) The part that's missing is to make Int32Interval half-open. It may also be possible to make them value types, in which case some or all uses of Int32Interval could be the BCL Range instead.

[SuuperW]

What is the advantage of this?
How is this simpler than the previous implementation, aside from removing unused code?
Why is Int32Interval closed while Int64Interval is half-open? EDIT: You said above that changing that is "missing". I say change it before merging (if it's going to ever be merged).

[SuuperW]

If you want this merged prior to my PR, address my comments and get it merged.