Consider adding a `ContainsMatching(func(T) bool)` method

[autarch]

It would be nice if there was a way to check whether or not the set contains something that matches in a more complex way than just equality.

For example:

import mapset "github.com/deckarep/golang-set/v2"

type Thing struct {
    name string
    size uint64
}

func (t Thing) String() string {
    return t.name
}

var (
    Thing1 = Thing{"foo", 42}
    Thing2 = Thing{"bar", 43}
)

set := mapset.NewSet(Thing1, Thing2)

if set.ContainsMatching(func(t Thing) bool { return t.String() == "foo" }) {
    ...
}

I'm not sure if ContainsMatching is the best name.

[ryclarke]

I like this idea, and for brainstorming method names set.Match() seems like a good fit IMO.