Add historical variant for Vietnamese i-hook

[KrasnayaPloshchad]

On this article I saw the Dictionarium Annamiticum (i.e. “Dictionary of Vietnamese Language”) have a variant for i-hook, in this case the dot remain unremoved, the hook is lowered and shift to right side. This could be implemented in two ways: 1) add proper mark attachment over combining dot above, 2) implement historical alternate to ỉ.