Keep scroll view content inset adjustment

[gim-]

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PR Summary

This fixes the issue for non-inverted table views when navigation bar was overlaying it. It was caused by _tableView.contentInsetAdjustmentBehavior being set to UIScrollViewContentInsetAdjustmentNever. I added a new method slk_updateInsetAdjustmentBehavior which updates adjustment behavior when isInverted field is mutated and sets an appropriate adjustment type based on the new value.

Related Issues

Fixes #642
Related to change from #631

[dzenbot]

Great fix @gim- !
I tested on simulator and device, and against the iPhoneX branch and it works like a charm! Thank you.