DM-42065: Move Object::getI into library body

[mwittgen]

No description provided.

[cmsaunders]

I'm curious why it's not necessary to move other similar methods like getD, but if this works it's fine with me to forward as is.

[mwittgen]

I'm curious why it's not necessary to move other similar methods like getD, but if this works it's fine with me to forward as is.

There might be more methods. If the member function defined in the astshim header
generates no references to ast, it can stay
defined in the header. Or if the including code does not use a member function from the
astshim header fille.