New API to get open identifers across entire library

**Is your feature request related to a problem? Please describe.**
`H5F_get_obj_ids` and `H5F_get_obj_count` consider transient datatypes to be objects only when using the `H5F_OBJ_ALL` flag. This makes them useful for retrieving and closing all open identifiers, but is inconsistent with library semantics.

**Describe the solution you'd like**
`H5F_get_obj_ids` and `H5F_get_obj_count` should only operate on objects that exist on files. A new API should be added to provide the "get all ids that need to be closed" functionality - either a new flag to these functions, or a new API call. Either way, this would be a breaking API change, so it won't go in until the next major release (1.15).

The work for this change is on [feature/h5f_get_obj_rework](/HDFGroup/hdf5/tree/feature/h5f_get_obj_rework). Currently, it changes the existing functions to not count transient datatypes in any case, but doesn't include any way to get all open ids.