Rename UTF16PtrToString and BasicStringToString.

* UTF16PtrToString -> LpOleStrToString
* BasicStringToString -> BStrToString

The new names are based on the standard Windows type aliases
that these functions are meant to work with (LPOLESTR and BSTR).

UTF16PtrToString still exists (as an alias for LpOleStrToString)
to ensure compatibility with other libraries that might be calling
this method, since it part of the public API.