Improve MutationObserver

- Fix get_removedNodes (it was returning addedNodes)
- get_removedNodes and get addedNodes now return references
- used enum for dispatching and clean up dispatching in general
- Remove MutationRecords and simply return an array
  - this allows the returned records to be iterable (as they should be)
  - jsruntime ZigToJs will now map a Zig array to a JS array
-Rely on default initialize of NodeList
-Batch observed records
 - Callback only executed when call_depth == 0
 - Fixes crashes when a MutationObserver callback mutated the nodes being
   observes.
 - Fixes some WPT issues, but Netsurf's mutationEventRelatedNode does not
   appear to be to spec, so most tests fail.
 - Allow zig methods to execute arbitrary code when call_depth == 0
   - This is a preview of how I hope to make XHR not crash if the CDP session
     ends while there's still network activity

Author: karlseguin

src/browser/dom/css.zig

@@ -49,7 +49,7 @@ const MatchAll = struct {
     fn init(alloc: std.mem.Allocator) MatchAll {
         return .{
             .alloc = alloc,
-            .nl = NodeList.init(),
+            .nl = .{},
         };
     }
 
@@ -62,7 +62,8 @@ const MatchAll = struct {
     }
 
     fn toOwnedList(m: *MatchAll) NodeList {
-        defer m.nl = NodeList.init();
+        // reset it.
+        defer m.nl = .{};
         return m.nl;
     }
 };