dillon1000/react

[other] Change instrumentation to use an optional gating identifier; record filepath

Internal rollout currently has a good number of test failures. 
`enableEmitInstrumentForget` can help developers understand which functions / 
files they should look at: 

``` 

// input 

function Foo() { 

userCode(); 

// ... 

} 

// output 

function Foo() { 

if (__DEV__ && inE2eTestMode) { 

logRender("Foo", "/path/to/filename.js"); 

} 

const $ = useMemoCache(...); 

userCode(); 

} 

```