This new import option will allow users to chose if we merge USD prims
with their Xform parent.
Given a USD like:
```
def Xform "MyObject"
{
def Mesh "MyObject_LOD0"
{
}
}
```
When the option is set to True (existing default), only the mesh will be
imported and its parent Xform transformation will be baked into the
Mesh.
```
# In blender after import
- MyObject_LOD0 (Mesh)
```
When the option is set to False, the parent Xform will always be
imported as an Empty object:
```
# In blender after import
- MyObject (Empty)
├─ MyObject_LOD0 (Mesh)
```
Co-authored-by: Odréanne Breton <odreanne.breton@ubisoft.com>
Co-authored-by: Sttevan Carnali Joga <sttevan.carnali-joga@ubisoft.com>
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