BIM: fix SwitchWB preference by switching to BIM WB

Fixes #14680.

src/Mod/BIM/Resources/ui/preferencesNativeIFC.ui

@@ -100,10 +100,10 @@
       <item>
        <widget class="Gui::PrefCheckBox" name="checkBox_3">
         <property name="toolTip">
-         <string>If this is checked, the workbench specified in Start preferences will be loaded after import</string>
+         <string>If this is checked, the BIM workbench will be loaded after import</string>
         </property>
         <property name="text">
-         <string>Switch workbench after import</string>
+         <string>Switch to BIM workbench after import</string>
         </property>
         <property name="prefEntry" stdset="0">
          <cstring>SwitchWB</cstring>

src/Mod/BIM/nativeifc/ifc_import.py

@@ -111,9 +111,7 @@ def insert(
     fsize = round(os.path.getsize(filename) / 1048576, 2)
     print("Imported", os.path.basename(filename), "(", fsize, "Mb ) in", endtime)
     if FreeCAD.GuiUp and switchwb:
-        from StartPage import StartPage
-
-        StartPage.postStart()
+        FreeCADGui.activateWorkbench("BIMWorkbench")
     return document