No longer hide exceptions from coerce method

[nomadium]

Hi folks,

This is another feature targeting Ruby 2.5 [1]:

• Numerical comparison operators (< ,<=, >=, >) no longer rescue exceptions of #coerce. Return nil in #coerce if the coercion is impossible.

• Integer#step does no longer rescue exceptions when given a step value which cannot be compared with #> to 0.

• Range#initialize no longer rescue exceptions when comparing begin and end with #<=> and raise a "bad value for range" ArgumentError but instead let the exception from the #<=> call go through.

All of these from feature #7688 [2].

Note: The tests are copied from MRI.

Thanks for your review and feedback.

1. #4876
2. https://bugs.ruby-lang.org/issues/7688