TreeBuilder - add #assert_type
TreeBuilder - add #assert_type

used in x_get_tree_custom_kids to verify assumptions about the type
(transferred from ManageIQ/manageiq@d4209e45e15edc88240569a6f425fdb3c256a5b1)

ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic