Bug 1896516 Part 5 - Fix build errors after including ScrollContainerFrame.h under dom/animation/. r=layout-reviewers,boris

This is a preparation to remove `#include "nsIScrollableFrame.h"` for
ScrollTimeline.cpp and ViewTimeline.cpp.

Move the implementation of `nsListControlFrame::GetMultiple()` to cpp. Keeping
it inline requires adding `#include "mozilla/dom/Element.h"` in the header, and
I don't feel the method is hot enough to be inlined.

Differential Revision: https://phabricator.services.mozilla.com/D211492

layout/generic/ScrollContainerFrame.cpp

@@ -96,6 +96,7 @@
 #include "mozilla/layers/ScrollLinkedEffectDetector.h"
 #include "mozilla/Unused.h"
 #include "MobileViewportManager.h"
+#include "TextOverflow.h"
 #include "VisualViewport.h"
 #include "WindowRenderer.h"
 #include <algorithm>