Fix test events not writable

[oluwatimio]

Problem

Changes were made to custom elements to use dispatchEvent https://github.com/shop/world/pull/93582 and standard DOM Events.

The issue is that these Event objects are not writable in tests

Error: Uncaught [TypeError: Cannot set property target of [object Event] which has only a getter]

Coming from remote-dom/polyfill

I asked Claude code to explain why this is happening in our test environment and here's the explanation

The issue occurs because of a mismatch between two different Event implementations:

1. Native DOM Events (created by userEvent.click() in tests): These have
   read-only properties like target, currentTarget, and eventPhase as defined by
   the DOM specification.

2. Polyfilled Events (from remote-dom): These define these properties as
   writable (like target: EventTarget | null = null on line 41).

When your tests run userEvent.click(), it creates a native DOM Event object,
but then the remote-dom polyfill's dispatchEvent method tries to modify
properties on that native event as if it were a polyfilled event.

The DOM specification defines these properties as read-only getters:

• Event.target - read-only, set when the event is dispatched
• Event.currentTarget - read-only, changes as event bubbles through DOM
• Event.eventPhase - read-only, indicates capture/target/bubble phase

So when the polyfill code tried to do:
event.target = this; // ❌ TypeError: Cannot set property target
event.currentTarget = currentTarget; // ❌ TypeError: Cannot set property
currentTarget
event.eventPhase = phase; // ❌ TypeError: Cannot set property
eventPhase

it failed because these are read-only on native events.

The try-catch blocks now allow the polyfill to work with both types of events

• it will set the properties on polyfilled events (where they're writable)
  and gracefully skip setting them on native events (where they're already
  correctly set by the browser).