Various memory measurement improvements (#36834)

The two significant changes here are 1) a commit that frees memory used
to perform memory reporting once the reporting is complete, 2) memory
reporting for the system font service. There are various other commits
that remove `#[ignore_malloc_size_of]` attributes for data that we are
now able to measure, but they do not significantly change our
measurements when testing servo.org.

Testing: Comparing the output of about:memory on servo.org.

---------

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

components/script/dom/bindings/cell.rs

@@ -10,6 +10,7 @@ pub(crate) use std::cell::{Ref, RefCell, RefMut};
 
 #[cfg(feature = "refcell_backtrace")]
 pub(crate) use accountable_refcell::{Ref, RefCell, RefMut, ref_filter_map};
+use malloc_size_of::{MallocConditionalSizeOf, MallocSizeOfOps};
 #[cfg(not(feature = "refcell_backtrace"))]
 pub(crate) use ref_filter_map::ref_filter_map;
 
@@ -24,6 +25,12 @@ pub(crate) struct DomRefCell<T> {
     value: RefCell<T>,
 }
 
+impl<T: MallocConditionalSizeOf> MallocConditionalSizeOf for DomRefCell<T> {
+    fn conditional_size_of(&self, ops: &mut MallocSizeOfOps) -> usize {
+        self.value.borrow().conditional_size_of(ops)
+    }
+}
+
 // Functionality specific to Servo's `DomRefCell` type
 // ===================================================