**Almost all shapechangers leave type unchanged.  Metallic dragons, though, *do* change their type.**

"Statistic," as a defined term, is spelled out on MM pp.6-11. The second element spelled out is "Type," of which both Celestial/Giant and Humanoid are instances. So which stays?

The Coautl's and Deva's *change shape* abilities specify that they retain their statistics except for a few callouts which do not include type. Since their Celestial type is a statistic they retain it and are still Celestial while in humanoid *form*.

The Oni's *change shape* ability specifies that the only statistic to change is size. Since type does not change, the Oni is still Giant while in humanoid *form.*

For completeness, the Quasit, Yochlol, Imp, Doppelganger, various weres, Mimic, Slaadi, Incubus/Succubus, Vampire, and various Yuan-ti are the other shapechangers in the MM. The Night Hag and Lizardfolk Shaman also *change shape* (ability) without being shapechangers (tag). All shapechange with similar verbiage to one of the samples above and so all retain their type.

Metallic Dragons' *Change Shape* ability does change type, as spelled out in their ability description.