[Upstream] deal_provider_collateral_bounds improvements.

[ruseinov]

1. Take a more readable approach for the method.

2. Perhaps introduce that same method for actors v8..v10.

    You're welcome to propose a change in the upstream https://github.com/filecoin-project/builtin-actors to address readability.
   

Originally posted by @LesnyRumcajs in #272 (comment)