Remove IPDFSDK_AnnotHandler::Annot_OnLoad().

Instead of going through CPDFSDK_AnnotHandlerMgr::Annot_OnLoad()
and IPDFSDK_AnnotHandler::Annot_OnLoad(), implement
CPDFSDK_Annot::OnLoad() as a virtual method, with an override in
CPDFSDK_Widget, and call that directly.

Change-Id: Ibc687d1254fc7c0b366d136d70f62f002bbe606a
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/92191
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/fpdfsdk/cpdfsdk_widget.h b/fpdfsdk/cpdfsdk_widget.h
index 2b373a1..17ddc52 100644
--- a/fpdfsdk/cpdfsdk_widget.h
+++ b/fpdfsdk/cpdfsdk_widget.h
@@ -49,6 +49,7 @@
   ~CPDFSDK_Widget() override;
 
   // CPDFSDK_BAAnnot:
+  void OnLoad() override;
   CPDF_Action GetAAction(CPDF_AAction::AActionType eAAT) override;
   bool IsAppearanceValid() override;
   int GetLayoutOrder() const override;