Import userProperties with MayaUSDImport

[BigRoy]

Is your feature request related to a problem? Please describe.

I have a Cube prim with a user property string attribute, for example:

custom string userProperties:customId = "hello:world"

When importing this with mayaUSDImport the attribute does not appear on the mesh or transform.

It's unclear to me what flag I should be passing to import the user properties as custom attributes on the import.

Describe the solution you'd like

Either default behavior should import the user properties or a flag importUserProperties would be added to enable it.

Describe alternatives you've considered

A python chaser could be implemented - however as far as I know it'd be non-trivial to generate the correct attribute type with the valid time-samples, etc. - which could be trivialized with UsdMayaReadUtil::ReadUsdAttribute() exposed to Python API as came up as a request here.

Additional context

The same 'issue' is also present in "Edit as Maya data" where it does not expose the user properties to the user for altering values.

Interestingly enough user properties are exposed however in a Maya USD Proxy with the UFE selection, e.g.:

[BigRoy]

Just wanted to note that custom primvars do get imported.
This gets imported:

    custom int primvars:myOtherValue = 1

This does not:

    custom int userProperties:myValue = 1

Note that the primvar one also works if it's not custom.

[maya-usd-git-sync]

Issue synced internally to EMSUSD-833