dillon1000/react

[hoisting][patch] use Babel identifier apis in BuildHIR hoisting logic

--- 

Three functional changes: 

- Instead of visiting all identifier references, explicitly traverse only 
function decls/exprs. This avoids bugs like accidentally hoisting inline 
references 

```js 

// input 

const x = identity(y); 

const y = 2; 

// lowered HIR before this PR (simplified) 

[0] DeclareContext HoistedConst y$0 

[1] LoadContext y$0 

[2] StoreLocal Const x$5 = identity([1]) 

``` 

- Rely on `isReferencedIdentifier()` instead of manually checking member 
properties / assignments, which is error prone 

```js 

// added fixture hoisting-repro-variable-used-in-assignment 

const callbk = () => { 

// before this PR, we skip hoisting x because it's part of a declaration 

const copy = x; 

return copy; 

}; 

const x = 2; 

return callbk(); 

``` 

- Visit lvalues after rvalues. This allows for recursive self-references (e.g. 
factorial) 

From the Babel side, this change relies heavily on babel's scope binding 
resolution logic. My understanding is: 

- Babel guarantees node objects are uniqued (`node1 === node2` <--> node1 and 
node2 are the same node in the ast) 

- Each binding has exactly one `bindingIdentifier` (`binding.identifier`, 
`getBindingIdentifier`, etc) which is identifier node @ its declaration site 

```js 

// x is a binding identifier 

const x = 2; 

// foo is a binding identifier 

function foo() { 

} 

// param is a binding identifier 

(param) => {...} 

// this bar is a binding identifier 

let bar; 

// but not this bar 

bar = 2; 

```