fix(core): imported element transform to class

[idoros]

This PR fixes an edge case of an imported element type selector (originally defined as type and not class) being transformed as a class selector:

/* origin.st.css */
Part {} /* defined as an "custom" element selector*/

/* entry.st.css */
@st-import [Part as ImportedPart] from './origin.st.css';

ImportedPart {} /* should transfrom to "Part", but wrongly changes to ".origin__Part" */

Notice that selectors like this are not namespaced and should be discouraged.