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/request.rs

@@ -108,7 +108,7 @@ impl Request {
 }
 
 fn net_request_from_global(global: &GlobalScope, url: ServoUrl) -> NetTraitsRequest {
-    RequestBuilder::new(url, global.get_referrer())
+    RequestBuilder::new(global.webview_id(), url, global.get_referrer())
         .origin(global.get_url().origin())
         .pipeline_id(Some(global.pipeline_id()))
         .https_state(global.get_https_state())