The property actually had a default, but defined via
`RNA_def_property_float_default` [**RNA** defaults handle highlevel (UI)
stuff like "Reset to Default", but is not in effect when creating new
data/editors].
For this to work, we now define the default in **DNA**
(Also corrects the mismatch in value in this particular case)
NOTE: other editors also handle "defaults" in `SpaceLink` creation functions
in their respective space_XXX.cc files, so that is another system to look at.
NOTE: there might be many more cases that could benefit from moving the
default from RNA (or `SpaceLink` creation functions) to DNA, or possibly even
doing this via other alternatives like supporting C++ in-class member initializers
in makesdna, goal is the same: having a single "source of truth".
But going over these will be for another time...
Pull Request: https://projects.blender.org/blender/blender/pulls/131735
5e5f2d2048