Possible improvements for `Int8/16/32/64`

[luc-blaeser]

Possible improvements for Int8.mo, Int16.mo, Int32.mo, and Int64:

• Support matchers with Int8/16/32/64/Nat8/16/32/64/Float/Order Testable.
• Inconsistent naming of functions, e.g. bitrotLeft() (instead of bitRotLeft()).
• Inconsistent type of second argument in bit operations: bitshiftLeft() uses Int64 but bittest() uses Nat.

Already fixed by PR https://github.com/dfinity/motoko-base/pull/478:

• Minimum value and maximum value constants are missing.
• bitnot() has a superfluous second argument: bitnot(x, y) should be bitnot(x).