A single `make_dimension` handles three types of dimensions,
(1) simple linear, (2) linear linked to an object, and (3) linked
to a circular edge.
So, we provide two new functions, `make_linear_dimension`
and `make_linear_dimension_obj`, to handle the first two cases.
In this way we can check the input parameters much better.
We adjust the `Draft_Dimension` Gui Command accordingly.
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