Add support for iterating over map data slab elements

[turbolent]

Description

Mostly useful for debugging.

TODO:

• Tests. IDK how to manually create a map data slab, it seems like the construction is not exported
• Error wrapping. The PopIterate functions sometimes wrap, sometimes have comments stating wrapping is not necessary. It is not quite clear to me

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[turbolent]

The tests looks good, thank you for adding them Faye!