map & set multibinding

[luozejiaqun]

Implement map & set multibinding just like dagger2.
Here is some implementation details:

Every MapMultibinding & SetMultibinding will involve 3 definitions:

1. the multibinding itself whose qualifier is mapMultibindingQualifier or setMultibindingQualifier
2. the element in multibinding whose qualifier is multibindingValueQualifier (use mapMultibindingQualifier/setMultibindingQualifier as prefix)
3. the MultibindingIterateKey which used to retrieve all elements, the key's qualifier is multibindingIterateKeyQualifier (also use mapMultibindingQualifier/setMultibindingQualifier as prefix)

When getting specific element from map multibinding, the map multibinding will try to retrieve the element through multibindingValueQualifier;
When getting all elements from map or set multibinding, the multibinding will first try to get all MultibindingIterateKey and filter based on qualifier prefix, and then retrieve each element through multibindingValueQualifier.

The known problems:

1. the multibinding qualifier can't be null, since it's qualifier will be used as prefix of element & iterate key
2. the map multibinding doesn't support null as a key
3. the elements order of multibiding is different with the order of element difinitions (there are ways to keep them in same order, but i don't think this is necessary)

And just like dagger2, multibinding is inherited (because MultibindingIterateKey can be retrieved from getAll), current scope's multibinding can get all elements that define in linked scope.

Here are some use case:

module {
    intoMap<String, Simple.ComponentInterface1>("keyOfComponent1") {
        Simple.Component1()
    }
    intoMap<String, Simple.ComponentInterface1>("keyOfComponent2") {
        Simple.Component2()
    }

    intoSet<Simple.ComponentInterface1> {
        Simple.Component1()
    }
    intoSet<Simple.ComponentInterface1> {
        Simple.Component2()
    }
}

val map: Map<String, Simple.ComponentInterface1> = koin.getMapMultibinding()
val set: Set<Simple.ComponentInterface1> = koin.getSetMultibinding()

issue #772

[arnaudgiuliani]

Looks interesting, will check for 4.1 👍