Fix duplicate stacking context creation for anonymous Flows

Anonymous nodes were previously creating duplicate stacking contexts,
one for each node in the anonymous node chain. This change eliminates
that for tables.

Additionally the use of stacking context ids based on node addresses is
no longer necessary since stacking contexts no longer control scrolling.
This is the first step in eliminating the dependency between node
addresses and ClipScrollNodes which causes issues like #16425.

components/gfx_traits/lib.rs

@@ -42,10 +42,9 @@ impl StackingContextId {
         StackingContextId(0)
     }
 
-    /// Returns a new sacking context id with the given numeric id.
-    #[inline]
-    pub fn new(id: u64) -> StackingContextId {
-        StackingContextId(id)
+    pub fn next(&self) -> StackingContextId {
+        let StackingContextId(id) = *self;
+        StackingContextId(id + 1)
     }
 }