Support package names shadowing type identifiers

SystemVerilog allows a package declaration to use a name that is also visible
as a type identifier. The lexer reports such names as `TYPE_IDENTIFIER` before
the package has been installed, which made constructs such as:

    package p;
      typedef int T;
    endpackage
    import p::*;
    package T;
    endpackage

fail in the package declaration grammar.

Package declarations do not have the local type/name ambiguity that exists for
variable, net, or parameter declarations. After the optional lifetime the next
token is always the package name. Use `identifier_name` so a
`TYPE_IDENTIFIER` token can be accepted as the package name.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>

parse.y

@@ -2359,7 +2359,7 @@ open_range_list /* IEEE1800-2005 A.2.11 */
   ;
 
 package_declaration /* IEEE1800-2005 A.1.2 */
-  : K_package lifetime_opt IDENTIFIER ';'
+  : K_package lifetime_opt identifier_name ';'
       { pform_start_package_declaration(@1, $3, $2); }
     timeunits_declaration_opt
       { pform_set_scope_timescale(@1); }