Adjust export semantics for WebPerformance symbols (#41300)

Summary:
Pull Request resolved: #41300

## Changelog:
[Internal] -
Makes the corresponding module exports more uniform.

Reviewed By: rubennorte

Differential Revision: D50960468

fbshipit-source-id: 11ae849daeba2be38604bed4c678d37188ad1f78

Author: rshest

packages/react-native/Libraries/WebPerformance/PerformanceEventTiming.js

@@ -20,7 +20,7 @@ export type PerformanceEventTimingJSON = {
   ...
 };
 
-export class PerformanceEventTiming extends PerformanceEntry {
+export default class PerformanceEventTiming extends PerformanceEntry {
   processingStart: HighResTimeStamp;
   processingEnd: HighResTimeStamp;
   interactionId: number;

packages/react-native/Libraries/WebPerformance/PerformanceObserver.js

@@ -13,6 +13,7 @@ import type {HighResTimeStamp, PerformanceEntryType} from './PerformanceEntry';
 import warnOnce from '../Utilities/warnOnce';
 import NativePerformanceObserver from './NativePerformanceObserver';
 import {PerformanceEntry} from './PerformanceEntry';
+import PerformanceEventTiming from './PerformanceEventTiming';
 import {
   performanceEntryTypeToRaw,
   rawToPerformanceEntry,
@@ -332,3 +333,5 @@ function union<T>(
 function difference<T>(a: $ReadOnlySet<T>, b: $ReadOnlySet<T>): Set<T> {
   return new Set([...a].filter(x => !b.has(x)));
 }
+
+export {PerformanceEventTiming};

packages/react-native/Libraries/WebPerformance/RawPerformanceEntry.js

@@ -15,7 +15,7 @@ import type {
 import type {PerformanceEntryType} from './PerformanceEntry';
 
 import {PerformanceEntry} from './PerformanceEntry';
-import {PerformanceEventTiming} from './PerformanceEventTiming';
+import PerformanceEventTiming from './PerformanceEventTiming';
 
 export const RawPerformanceEntryTypeValues = {
   UNDEFINED: 0,