dillon1000/react

Validate frozen lambdas are actually frozen

Adds validation to reject freezing mutable lambdas, since lambdas cannot _be_ 
frozen, they're either frozen or not. Example invalid code: 

```javascript 

function Component(props) { 

const x = {value: ""}; 

const onChange = (e) => { 

// MUTATION!!!!! 

x.value = e.target.value; 

setX(x); 

}; 

return <input value={x.value} onChange={onChange} />; 

} 

``` 

Note that there is a separate issue in which we are not detecting lambdas that 
would definitely modify immutable values. We may need to distinguish 
ConditionallyCapture (captures if the value is mutable, otherwise readonly) from 
Capture (definitely mutates) in order to make that case work. But already this 
validation helps prevent some invalid code.