Deprecate .set .list and .map in favour of asList, asSet and asMap

[passsy]

Deprecated KtList.list: List, added KtList.asList(): List
Deprecated KtSet.set: Set, added KtSet.asSet(): Set
Removed KtMap.map: Map, added KtMap.asMap(): Map

Added KtMap<K, V>.iter: Iterable<MapEntry<K, V>> which makes it possible KtMaps in for-loops.

final pokemon = mutableMapFrom({1: "Bulbasaur", 2: "Ivysaur"});

for (final p in pokemon.iter) {
  print("${p.key} -> ${p.value}"); 
}

// 1 -> Ditto
// 2 -> Ivysaur

fixes #79

[codecov]

Codecov Report

Merging #85 into master will increase coverage by 0.11%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #85      +/-   ##
==========================================
+ Coverage   99.71%   99.83%   +0.11%     
==========================================
  Files          40       41       +1     
  Lines        1774     1826      +52     
==========================================
+ Hits         1769     1823      +54     
+ Misses          5        3       -2

Impacted Files	Coverage Δ
lib/src/collection/impl/iterator.dart	100% <ø> (ø)	⬆️
lib/src/collection/kt_map.dart	100% <ø> (ø)	⬆️
lib/src/collection/kt_list.dart	100% <ø> (ø)	⬆️
lib/src/collection/kt_list_mutable.dart	100% <ø> (ø)	⬆️
lib/src/collection/kt_map_mutable.dart	100% <ø> (ø)	⬆️
lib/src/collection/kt_set.dart	100% <ø> (ø)	⬆️
lib/src/collection/kt_set_mutable.dart	100% <ø> (ø)	⬆️
...rc/collection/impl/dart_unmodifiable_set_view.dart	100% <100%> (ø)
lib/src/collection/impl/map_mutable.dart	100% <100%> (+1.44%)	⬆️
lib/src/collection/impl/set.dart	100% <100%> (ø)	⬆️
... and 11 more

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