This PR splits `Std.Classes.Ord` into `Std.Classes.Ord.Basic` (with few
imports) and `Std.Classes.Ord.SInt` and `Std.Classes.Ord.Vector`. These
changes avoid importing `Init.Data.BitVec.Lemmas` unnecessarily into
various basic files.
As the new import-only file `Std.Classes.Ord` imports all three of
these, end-users are not affected.
