Add onDeepLink EventHandler to h5vcc_runtime IDL

[zhongqiliang]

1. Modify h_5_vcc_runtime.idl to include an onDeepLink event handler.
2. Define a custom event named DeepLinkEvent to be used by the onDeepLink handler. This event will carry the deep link information.
3. When a JavaScript application registers the onDeepLink event handler. Attempt to retrieve the initial deep link using the GetInitialDeepLink() mojom API. If the retrieved value is not empty, immediately dispatch a DeepLinkEvent with the initial deep link data."

Sample javascript code for register the onDeepLink callback.

window.h5vcc.runtime.onDeepLink = (event) => {
  if (event.type === 'deeplink') {
    console.log("Deeplink event received!");
    console.log("Deeplink URL:", event.url);
  }
};

Tested on devtools. https://screenshot.googleplex.com/AymzZtjCxUYZg2G

b/374147993

[zhongqiliang]

Working on the web test.

[yell0wd0g]

Looking pretty good! A few comments here and there.

[yell0wd0g]

I don't oppose these changes anymore but I'll ask for another pass at the JS test 🙏

[hlwarriner]

Left two minor comments but otherwise lgtm, thanks!

[andrewsavage1]

Would this type of event handler change be what we follow for all of our event handlers? I.e. would the signature for H5vccRuntime.onPause end up changing a similar way?

[hlwarriner]

@zhongqiliang I'm seeing a crash on a devel linux build at https://github.com/youtube/cobalt/blob/main/third_party/blink/renderer/core/trustedtypes/trusted_type_policy_factory.cc#L77, related to onDeepLink. Can you please take a look? We might need to revert or fix forward.