Improve transient storage support

[smonicas]

This PR does the following:

• Compute the storage layout for both transient and storage
• API changes in the Contract class
  • state_variables_ordered: All state variables including constants and immutables. Same as before
  • storage_variables_ordered: Only state variables with storage location
  • transient_variables_ordered: Only state variables with transient location
  • Removed the unordered storage version called stored_state_variables as it adds complexity to the API, it's enough the ordered version independently if the order matters or not,
• Moved the is_stored property to the StateVariable class from the Variable class as it only makes sense for StateVariable, all the code was already using it after checking if the var is a StateVariable. Added the is_transient equivalent.
• Add the State column to the variable-order printer which will contain "storage" or "transient"
• Updated the upgradeability tool to also check the transient storage