Techs incorrectly excluded from `capacity_factor` via `map_tec_time`

It seems in [the GAMS formulation](https://github.com/iiasa/message_ix/blob/705f55f648ede9a9a927411a640d37620f354020/message_ix/model/MESSAGE/data_load.gms#L148) some technologies are omitted from `capacity_factor`, even though defined by the user. These technologies do not have `input`, `output` commodity defined and do not appear in `relation_activity`; that's why they are not in the set `map_tec_time`, and hence, mapped out from `capacity_factor` in this equation. I believe this is not correct, as some technologies can play a role with their capacity, e.g., in parameter `relation_total_capacity`, and should not be excluded from capacity equations if they don't have input/output commodity, or because not appearing in `relation_activity`.

Start with the GAMS formulation at message_ix/model/MESSAGE/data_load.gms line 148, then inspect how map_tec_time is built from input/output and relation_activity. Reproduce a technology without those entries and verify that capacity_factor is still available for capacity equations, including relation_total_capacity.

Written by the indexing model from the issue text.