EMSUSD-1719 units prefs during import

When using the overwrite-prefs method to change the units during import, we need to compare with teh Maya UI units, not the internal units. (When using the scaling method, we are scaling to internal units.)

lib/mayaUsd/fileio/jobs/readJob.cpp

@@ -495,8 +495,13 @@ void UsdMaya_ReadJob::_ConvertUpAxisAndUnits(const UsdStageRefPtr& stage)
 
     // Convert units if required and different between Maya and USD.
     const bool convertUnits = mArgs.unit;
-    conversion.mayaMetersPerUnit
-        = UsdMayaUtil::ConvertMDistanceUnitToUsdGeomLinearUnit(MDistance::internalUnit());
+    // Note: when changing preference, we need to compare to the UI units.
+    //       When adding scaling transforms, we need to compare to internal units.
+    const MDistance::Unit mayaUnits
+        = (mArgs.axisAndUnitMethod == UsdMayaJobImportArgsTokens->overwritePrefs)
+        ? MDistance::uiUnit()
+        : MDistance::internalUnit();
+    conversion.mayaMetersPerUnit = UsdMayaUtil::ConvertMDistanceUnitToUsdGeomLinearUnit(mayaUnits);
     conversion.usdMetersPerUnit = UsdGeomGetStageMetersPerUnit(stage);
     conversion.needUnitsConversion
         = (convertUnits && (conversion.mayaMetersPerUnit != conversion.usdMetersPerUnit));