Add SparseArrays forEach extensions

[deva666]

feature #223

[Dragas]

In my opinion, it should follow the iterator implementation, not for(i in 0..size()-1), as that would prevent possible discrepancies if the said array modifies itself.
That said, current implementation does seem to be prone to IndexOutOfBoundsException if the former happens by self modification as well as ConcurrentModificationException

[Miha-x64]

I think this implementation is OK, because SparseArrays have no iterators and thus it will be impossible to check for comodification fast and clearly. Unlike iterators, given extensions do not use any extra allocations, which is much appreciated in Android.
Also:
— you can use 0 until size instead of 0 .. size-1, this is less error-prone and more self-explanatory;
— it is also possible to implement forEachKey and forEachValue;
— there are also SparseArrayCompat and SimpleArrayMap, they could be iterated this way too.

[yanex]

Merged. Thank you!