Generic shift operations

[oscbyspro]

I'll add generic shift operations with appropriate paths to the Shift\<T> base implementation:

static func  <<=(instance: inout     Self, distance: some BinaryInteger)
static func  << (instance: consuming Self, distance: some BinaryInteger) -> Self 
static func  >>=(instance: inout     Self, distance: some BinaryInteger)
static func  >> (instance: consuming Self, distance: some BinaryInteger) -> Self

static func &<<=(instance: inout     Self, distance: some BinaryInteger)
static func &<< (instance: consuming Self, distance: some BinaryInteger) -> Self 
static func &>>=(instance: inout     Self, distance: some BinaryInteger)
static func &>> (instance: consuming Self, distance: some BinaryInteger) -> Self

[oscbyspro]

I found the lack of generic shifts annoying when I prototyped (#25).

[oscbyspro]

I'll also unify Shift\<T> and Shift\<T.Magnitude> as the latter.

[oscbyspro]

It also accepts Swift.Int distances because I needed to disambiguate integer literals...