Add immutable collections hierarchy with runtime/compiler/docs/tests

docs/Collection.md

@@ -6,6 +6,12 @@ Is a [Iterable] with known `size`, a finite [Iterable]:
         val size
     }
 
+`Collection` is a read/traversal contract shared by mutable and immutable collections.
+Concrete collection classes:
+
+- Mutable: [List], [Set], [Map]
+- Immutable: [ImmutableList], [ImmutableSet], [ImmutableMap]
+
 | name                   | description                                          |
 |------------------------|------------------------------------------------------|
 
@@ -16,4 +22,8 @@ See [List], [Set], [Iterable] and [Efficient Iterables in Kotlin Interop](Effici
 
 [Iterable]: Iterable.md
 [List]: List.md
-[Set]: Set.md
+[Set]: Set.md
+[Map]: Map.md
+[ImmutableList]: ImmutableList.md
+[ImmutableSet]: ImmutableSet.md
+[ImmutableMap]: ImmutableMap.md