better support for struct array parameters

This includes support for
- parsing dimensioned alias parameters
- flattening non-var decls with multiple packed dimensions
- converting arrays of structs
- inferring struct types for decls with initializations

test/basic/struct_array_param.v

@@ -0,0 +1,8 @@
+module top;
+  parameter foo_1 = { 3'b010, 2'b01, 4'b0000 };
+  parameter foo_0 = { 3'b001, 2'b00, 4'b0010 };
+    initial begin
+        $display(foo_0);
+        $display(foo_1);
+    end
+endmodule