cty: The documented definition and comparison logic of cty.Number is now
refined to acknowledge that its true range is limited only to values
that have both a binary floating point and decimal representation,
because cty values are primarily designed to traverse JSON serialization
where numbers are always defined as decimal strings.

In particular, that means that two cty.Number values now always compare
as equal if their representation in JSON (under cty's own JSON encoder)
would be equal, even though the decimal approximation we use for that
conversion is slightly lossy. This pragmatic compromise avoids confusing
situations where a round-trip through JSON serialization (or other
serializations that use the same number format) may produce a value that
doesn't compare equal to the original.

This new definition of equals should not cause any significant behavior
change for any integer in our in-memory storage range, but may cause
some fractional values to compare equal where they didn't before if they
differ only by a small fraction.