The current implementation goes like this
* default to a 0-1 range
* you can set `is_bidirectional` to get a -1/1 range
* if the slider is bidirectional the overshoot goes both ways, otherwise only on the positive side
The issue is that it is not possible to have a 0-1 range but overshoot both ways.
This is useful for example on the "Blend to Default" operator, where 0 means current position and 1 default.
But overshoot also makes sense for this operator since the other way just scales away from default.
So this patch:
* removes `is_bidirectional`
* adds `float range[2]` to `tSlider` and a setter for it
* rewrite some logic to handle arbitrary ranges
* split the `allow_overshoot` flag into one flag for either side
Pull Request: https://projects.blender.org/blender/blender/pulls/107406
c9b51591da