ENH: Use `dags` features instead of relying on own implementation

[MImmesberger]

As discussed in #780, we should rely more on features that dags already implemented. These need to be exposed first via a PR in dags.

The features we could use in GETTSIM are:

• QUALIFIED_NAME_DELIMITER (currently _qualified_name_delimiter): We will never use a different one than the one specified in dags.
• is_qualified_name (currently _is_qualified_name): Check whether a string is a qualified name. We currently do this in GETTSIM via QUALIFIED_NAME_DELIMITER in some_string.
• map_parameter (currently _map_parameter): Convert (simple or qualified) names to qualified names. This one could be useful in _get_tree_path_from_source_col_name that emulates this behavior.
• The types we defined in gettsim_typing are similar to the ones in dags.
• qualified_name_reducer and qualified_name_splitter.

[hmgaudecker]

All fixed and more in #841 / dags 0.3.0

[MImmesberger]

Closed via #841