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

[IsaacIsrael]

Summary

Fixes #54732

The Event class in src/private/webapis/dom/events/Event.js defines NONE, CAPTURING_PHASE, AT_TARGET, and BUBBLING_PHASE as both readonly instance fields and via Object.defineProperty without writable/configurable flags. When Hermes compiles these class fields, they become non-writable/non-configurable properties, causing a TypeError at instantiation time:

TypeError: Cannot assign to read-only property 'NONE'
    at Event (Event.js:53:4)
    at anonymous (WebSocket.js:258:63)
    at apply (native)
    at emit (EventEmitter.js:130:7)

This crashes whenever a WebSocket event fires (Metro dev connection, push notifications), and the unhandled TypeError propagates into any concurrent Promise chain — breaking fetch() uploads and other network operations.

Changes

1. Remove readonly from instance-level field declarations — the static properties are inherited via the prototype chain automatically, so explicit readonly instance declarations are unnecessary and cause the Hermes conflict.

2. Add writable: true, configurable: true to all 8 Object.defineProperty calls — allows event-target-shim (used by abort-controller / fetch()) to redefine these properties when needed.

3. Replace Event.NONE initializer with literal 0 — the [EVENT_PHASE_KEY] field initializer was referencing Event.NONE before Object.defineProperty defines it at the bottom of the file.

Changelog:

[GENERAL] [FIXED] - Fix TypeError "Cannot assign to read-only property 'NONE'" in Event class when using New Architecture with Hermes

Test Plan

1. Create a React Native 0.85+ app with New Architecture enabled
2. Make any fetch() request or open a WebSocket connection
3. Verify no TypeError: Cannot assign to read-only property 'NONE' is thrown
4. Verify event.NONE === 0, event.CAPTURING_PHASE === 1, event.AT_TARGET === 2, event.BUBBLING_PHASE === 3 still hold on Event instances