lua: add MsgPack encoding/decoding context to MsgPack objects

Extend the MsgPack object creation interface to push a MsgPack context
required for decoding tuples coming from IPROTO, the context ownership is
acquired by the new object to avoid copying (thus, a virtual `move`
function is added to the MsgPack context).

When a MsgPack context is owned by a MsgPack object, the lifetime of the
former is controlled by the latter, hence a virtual `destroy` function is
added to the MsgPack context.

Needed for #8147

NO_CHANGELOG=refactoring
NO_DOC=refactoring
NO_TEST=refactoring