Replace stallTrackingIntegration's JS polling with PerformanceObserver({type: 'longtask'})

[alwx]

stallTrackingIntegration detects main thread stalls with a JS-side polling timer. RN >=0.82 exposes PerformanceObserver with a native longtask entry type - evaluate replacing the polling approach with it.

[linear-code]

RN-782