Fix types of inserted constants

[arxenix]

I think another case where types are incorrect is in:

    function addTest(uint8 a, uint32 b) external pure returns(uint32){
        return a+b;
    }

because the lvalue type is automatically set to variable_left

slither/slither/slithir/convert.py

Line 365 in 5d6ab21

ir.lvalue.set_type(ir.variable_left.type)

but this isn't always correct, because type of uint X+uint Y should be uint max(X,Y) (same for int)