typefind: add a new method that also uses the file extension

typefind: add a new method that also uses the file extension

Add a method to perform get_range typefinding that also uses the
uri/location extension as an extra hint. It will first try to call the
typefind functions of the factories that handle the given extension. The result
is that in the common case, we only call one typefind function, which speeds up
the typefinding a lot.