edje: Add part_type_get API

edje: Add part_type_get API

For now I made this EO-only but this definitely could be expose in
legacy API as well.

This simply gives exact information about the type of part, after doing
a recursive search. Edit Edit doesn't do a recursive search, only a
direct one, which can yield invalid results (eg. RECT or NONE instead of
TEXT in case of "elm.units.max" for a slider).

@feature