Introduce maximum_size() to implement size_hint for set of values

[gui1117]

When implementing size_hint for a vector or a set we don't want to iterate on all the values to actually get a hint.
One way to do so would be to have two method one taking a value size_hint(&self) and another one taking no value maxium_size().

thus they would be used as such:

• maximum_size() used on set of values
• size_hint(&self) used on individual values,

size_hint(&self) (thought maybe renamed) would default implementation to maximum_size()