Merge to XFA: Add new public APIs to find the z-order for links and widgets.

- Implement FPDFLink_GetLinkZOrderAtPoint().
- Implement FPDFPage_FormFieldZOrderAtPoint().
- Mark FPDPage_HasFormFieldAtPoint() as deprecated.
- Modify CPDF_LinkList and CPDF_InterForm to support new APIs.
- Clean up dead code in CPDF_LinkList and CPDF_InterForm.

BUG=chromium:515837
R=jun_fang@foxitsoftware.com, tsepez@chromium.org

Review URL: https://codereview.chromium.org/1278053004 .

(cherry picked from commit 24fbf134d43a7ec4226de3db601f0a617bbe428b)

Review URL: https://codereview.chromium.org/1295893005 .
diff --git a/fpdfsdk/src/fpdfview_c_api_test.c b/fpdfsdk/src/fpdfview_c_api_test.c
index f96aec4..01789b4 100644
--- a/fpdfsdk/src/fpdfview_c_api_test.c
+++ b/fpdfsdk/src/fpdfview_c_api_test.c
@@ -54,6 +54,7 @@
     CHK(FPDFAction_GetURIPath);
     CHK(FPDFDest_GetPageIndex);
     CHK(FPDFLink_GetLinkAtPoint);
+    CHK(FPDFLink_GetLinkZOrderAtPoint);
     CHK(FPDFLink_GetDest);
     CHK(FPDFLink_GetAction);
     CHK(FPDFLink_Enumerate);
@@ -108,7 +109,9 @@
     CHK(FORM_OnKeyUp);
     CHK(FORM_OnChar);
     CHK(FORM_ForceToKillFocus);
-    CHK(FPDPage_HasFormFieldAtPoint);
+    CHK(FPDFPage_HasFormFieldAtPoint);
+    CHK(FPDPage_HasFormFieldAtPoint);  // DEPRECATED. Remove in the future.
+    CHK(FPDFPage_FormFieldZOrderAtPoint);
     CHK(FPDF_SetFormFieldHighlightColor);
     CHK(FPDF_SetFormFieldHighlightAlpha);
     CHK(FPDF_RemoveFormFieldHighlight);