Add type nesting rules for extern, parser, control, and package types

[jaehyun1ee]

I would like to propose a change to the spec following the discussion made in #1324.
This adds the cases for extern / parser / control / package types for the type nesting rule defined in section 7.2.8.

In summary,

• It disallows extern / parser / control / package types from being nested inside a header / header union / struct / tuple / list / header stack.
• It allows extern / parser / control / package to be aliased by typedef, but disallows for type.