Convert disk lights to spot light when cone:angle attribute is present

[TomMinor]

Describe the bug
Creating a spotlight via the tab menu (Lights >> Spot Light) will use 'Disk' as the default type:

When exported to .USD (and converted to .ASS with kick), the type is disk_light

disk_light
{
 name /lights/spotlight1
 matrix
 0.967461348 0.0116126118 -0.252752304 0
 -0.252959639 0.0227694027 -0.967208862 0
 -0.00547680212 0.999673307 0.0249660388 0
 0.0243682899 1.84101534 0.2631042 1
 color 1 1 1
 intensity 10
 exposure 0
 normalize off
 diffuse 1
 specular 1
 filters 2 1 NODE
NULL "/materials/arnold_materialbuilder1/gobo1"
 radius 0.706361651
}

This doesn't work with gobo light linking, which only works for spot_light/sphere light types.

Potential fix

Identify when the 'spotlight specific' attributes are set (i.e. cone:angle)
and set the light type to spot_light.

To Reproduce
Steps to reproduce the behavior:

1. Create a spotlight via the tab menu (Lights >> Spot Light)

2. Change the angle to something reasonable
   

3. Follow the light linking docs to attach a Gobo to the spotlight, e.g.
   

4. The render will show nothing
   

5. Change the spotlight type to 'Sphere' (or 'Point')
   

6. The render will now shot the light filter properly
   

Used Software Versions

• Houdini 19.5.569

[autodesk-oss-arnold-bot]

Issue synced internally to ARNOLD-13593