script: Reduce ScriptThread TLS usage (#38875)

We store a pointer to the ScriptThread singleton for a thread in
thread-local storage. While we don't have yet have profiles pointing to
this TLS access as a hot spot, we can remove a potential performance
footgun without a lot of effort by passing around small pieces of data
that we otherwise need to fetch from the ScriptThread.

Testing: Existing WPT is sufficient
Fixes: part of #37969

---------

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

components/script/dom/servoparser/html.rs

@@ -52,12 +52,14 @@ impl Tokenizer {
         fragment_context: Option<super::FragmentContext>,
         parsing_algorithm: ParsingAlgorithm,
     ) -> Self {
+        let custom_element_reaction_stack = document.custom_element_reaction_stack();
         let sink = Sink {
             base_url: url,
             document: Dom::from_ref(document),
             current_line: Cell::new(1),
             script: Default::default(),
             parsing_algorithm,
+            custom_element_reaction_stack,
         };
 
         let quirks_mode = match document.quirks_mode() {