script: Wrapping unsafe code in unsafe blocks for basic DOM types (#37997)

There is a new default cargo clippy lint, `unsafe_op_in_unsafe_fn`,
which requires unsafe code to be wrapped in unsafe blocks, even inside
functions marked as unsafe. The lint is disabled as much of our code
doesn't fulfill this contract. The thing itself is pretty useful in
order to gradually remove unsafety, so this change starts adding
`unsafe` blocks so we can eventually enable this lint.

Testing: This doesn't change behavior so existings tests should suffice.
Fixes: This is part of #35955.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/script/script_thread.rs

@@ -179,7 +179,7 @@ pub(crate) fn with_script_thread<R: Default>(f: impl FnOnce(&ScriptThread) -> R)
 pub(crate) unsafe fn trace_thread(tr: *mut JSTracer) {
     with_script_thread(|script_thread| {
         trace!("tracing fields of ScriptThread");
-        script_thread.trace(tr);
+        unsafe { script_thread.trace(tr) };
     })
 }