View modifier semantics

[bitbart]

Revise the semantics of TinySol so that functions declared as view cannot modify the state variables of the contract:

https://docs.soliditylang.org/en/latest/contracts.html#state-mutability

For example, in the contract:

contract C {
      uint x;
      function f() public view { x = 1; }
}

any call to f must revert, since it modifies the state variable x.