Do not check mutability when computing projections

[ehildenb]

The current logic for computing projections looks at the mutability of fields when reading them, which shouldn't be necessary as we should be allowed to read mutable fields (just not write them). So this removes the mutability check, which means the additional arguments FORCE and MUT are not needed for #projectUpdate. So we refactor the bits of state that aren't needed to be in a different KItem in the second position on the <k> cell.

In particular:

• Remove the checks on each rule of #projectUpdate which inspect the mutability of the read fields and the FORCE field.
• Pulls out the state that is no longer needed to actually compute the projection (the new value to write, and the FORCE) into a second KItem on the <k> cell, and re-wires the rules to use this when doing #setLocalValue.