Use spec-aligned process for resolving history handling during navigation (#34747)

Makes use of the is_initial_about_blank property on Document in order to
determine whether the navigation should create a history entry, or replace
the current history entry.

Signed-off-by: Shane Handley <shanehandley@fastmail.com>

components/script/script_thread.rs

@@ -3134,6 +3134,8 @@ impl ScriptThread {
             .as_ref()
             .map(|referrer| referrer.clone().into_string());
 
+        let is_initial_about_blank = final_url.as_str() == "about:blank";
+
         let document = Document::new(
             &window,
             HasBrowsingContext::Yes,
@@ -3148,6 +3150,7 @@ impl ScriptThread {
             referrer,
             Some(metadata.status.raw_code()),
             incomplete.canceller,
+            is_initial_about_blank,
             can_gc,
         );