Make is-approx DWIM when no tolerances are provided
Make is-approx DWIM when no tolerances are provided

When current version was designed, the default was chosen to abs-tol of 1-e5, with
reasoning behind that it would be easy for users to understand it (as compared with
rel-tol or some DWIM mechanism). While that goal was accomplished, when using the
function in real-world application, the abs-tol default proves to be nearly useless.
It's too small for large numbers and too large for small numbers, forcing the user to
specify manually. Moreover, rel-tol can't be used when $expected is zero, so the user
constantly has to think about which tolerances to plug into the function.

This commit restores the DWIMmy behaviour of old is_approx for the default case where
no tolerances are given: if $expected.abs() is smaller than 1e-6, use absolute
tolerance of 1e-5; else, use relative tolerance of 1e-6.

Both the existing Rakudo tests for this function and the entire stresstest passes with
these changes, but that's mostly due to undertesting (or in roast's case, no testing).
I looked at ecosystem usages and the function isn't used frequently. Both of those
suggest to me the impact of this change would be minimal, if not entirely non-existent.

lucasbuchala/rakudo,softmoth/rakudo,tony-o/rakudo,jonathanstowe/rakudo,MasterDuke17/rakudo,sjn/rakudo,nbrown/rakudo,nbrown/rakudo,awwaiid/rakudo,nbrown/rakudo,rakudo/rakudo,Gnouc/rakudo,sjn/rakudo,tbrowder/rakudo,jonathanstowe/rakudo,rakudo/rakudo,tony-o/rakudo,samcv/rakudo,rakudo/rakudo,usev6/rakudo,usev6/rakudo,softmoth/rakudo,lucasbuchala/rakudo,sjn/rakudo,jonathanstowe/rakudo,labster/rakudo,sjn/rakudo,usev6/rakudo,Gnouc/rakudo,lucasbuchala/rakudo,labster/rakudo,jonathanstowe/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,Gnouc/rakudo,salortiz/rakudo,softmoth/rakudo,salortiz/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,tony-o/rakudo,tbrowder/rakudo,samcv/rakudo,raydiak/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,usev6/rakudo,raydiak/rakudo,usev6/rakudo,softmoth/rakudo,labster/rakudo,salortiz/rakudo,nbrown/rakudo,nbrown/rakudo,rakudo/rakudo,Gnouc/rakudo,labster/rakudo,salortiz/rakudo,raydiak/rakudo,awwaiid/rakudo,rakudo/rakudo,salortiz/rakudo,samcv/rakudo,tony-o/rakudo,softmoth/rakudo,nbrown/rakudo,Gnouc/rakudo,MasterDuke17/rakudo,lucasbuchala/rakudo,samcv/rakudo,rakudo/rakudo,tony-o/rakudo,MasterDuke17/rakudo,salortiz/rakudo,lucasbuchala/rakudo,labster/rakudo,raydiak/rakudo,jonathanstowe/rakudo,awwaiid/rakudo,awwaiid/rakudo,awwaiid/rakudo,sjn/rakudo,Gnouc/rakudo,labster/rakudo,samcv/rakudo,tony-o/rakudo,tbrowder/rakudo