fix: make Event phase constants writable/configurable to prevent TypeError

The Event class defines NONE, CAPTURING_PHASE, AT_TARGET, BUBBLING_PHASE
as readonly instance fields and via Object.defineProperty without
writable/configurable flags. Hermes compiles these as non-writable,
causing TypeError at instantiation: Cannot assign to read-only property NONE.

This crashes on WebSocket events and propagates into fetch uploads.

Fix: remove readonly from instance fields, add writable+configurable to
Object.defineProperty calls, replace Event.NONE initializer with literal 0.

Fixes #54732

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: IsaacIsrael

packages/react-native/src/private/webapis/dom/events/Event.js

@@ -50,10 +50,10 @@ export default class Event {
   static readonly AT_TARGET: 2;
   static readonly BUBBLING_PHASE: 3;
 
-  readonly NONE: 0;
-  readonly CAPTURING_PHASE: 1;
-  readonly AT_TARGET: 2;
-  readonly BUBBLING_PHASE: 3;
+  NONE: 0;
+  CAPTURING_PHASE: 1;
+  AT_TARGET: 2;
+  BUBBLING_PHASE: 3;
 
   _bubbles: boolean;
   _cancelable: boolean;
@@ -70,7 +70,7 @@ export default class Event {
   [CURRENT_TARGET_KEY]: EventTarget | null = null;
 
   // $FlowExpectedError[unsupported-syntax]
-  [EVENT_PHASE_KEY]: boolean = Event.NONE;
+  [EVENT_PHASE_KEY]: boolean = 0;
 
   // $FlowExpectedError[unsupported-syntax]
   [IN_PASSIVE_LISTENER_FLAG_KEY]: boolean = false;
@@ -193,48 +193,64 @@ export default class Event {
 
 // $FlowExpectedError[cannot-write]
 Object.defineProperty(Event, 'NONE', {
+  writable: true,
+  configurable: true,
   enumerable: true,
   value: 0,
 });
 
 // $FlowExpectedError[cannot-write]
 Object.defineProperty(Event.prototype, 'NONE', {
+  writable: true,
+  configurable: true,
   enumerable: true,
   value: 0,
 });
 
 // $FlowExpectedError[cannot-write]
 Object.defineProperty(Event, 'CAPTURING_PHASE', {
+  writable: true,
+  configurable: true,
   enumerable: true,
   value: 1,
 });
 
 // $FlowExpectedError[cannot-write]
 Object.defineProperty(Event.prototype, 'CAPTURING_PHASE', {
+  writable: true,
+  configurable: true,
   enumerable: true,
   value: 1,
 });
 
 // $FlowExpectedError[cannot-write]
 Object.defineProperty(Event, 'AT_TARGET', {
+  writable: true,
+  configurable: true,
   enumerable: true,
   value: 2,
 });
 
 // $FlowExpectedError[cannot-write]
 Object.defineProperty(Event.prototype, 'AT_TARGET', {
+  writable: true,
+  configurable: true,
   enumerable: true,
   value: 2,
 });
 
 // $FlowExpectedError[cannot-write]
 Object.defineProperty(Event, 'BUBBLING_PHASE', {
+  writable: true,
+  configurable: true,
   enumerable: true,
   value: 3,
 });
 
 // $FlowExpectedError[cannot-write]
 Object.defineProperty(Event.prototype, 'BUBBLING_PHASE', {
+  writable: true,
+  configurable: true,
   enumerable: true,
   value: 3,
 });