Include WebViewId into EmbedderMsg variants where possible (#35211)

`EmbedderMsg` was previously paired with an implicit
`Option<WebViewId>`, even though almost all variants were either always
`Some` or always `None`, depending on whether there was a `WebView
involved.

This patch adds the `WebViewId` to as many `EmbedderMsg` variants as
possible, so we can call their associated `WebView` delegate methods
without needing to check and unwrap the `Option`. In many cases, this
required more changes to plumb through the `WebViewId`.

Notably, all `Request`s now explicitly need a `WebView` or not, in order
to ensure that it is passed when appropriate.

Signed-off-by: Delan Azabani <dazabani@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

components/script/dom/worklet.rs

@@ -652,6 +652,7 @@ impl WorkletThread {
         // TODO: Caching.
         let resource_fetcher = self.global_init.resource_threads.sender();
         let request = RequestBuilder::new(
+            None,
             script_url,
             global_scope.upcast::<GlobalScope>().get_referrer(),
         )