Conversion was only possible if the active object was editable &
selected, this complicated overriding the operator from Python
since it wasn't enough to override the selection & active-object.
Now it's possible to use bpy.ops.object.convert() from Python
overriding the selected_editable_objects only.
For users the difference isn't so significant:
- Having an active object is no longer required.
- It's possible there are no objects to operate on,
as previously the active object was used to check at least one
object could be converted, although this check wasn't fool-proof
as it didn't check the objects data-type.
Resolves#100664.
Ref !134728.
9e0c8a41cd