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

fpdfsdk/src/fpdfview_c_api_test.c

Index: fpdfsdk/src/fpdfview_c_api_test.c
diff --git a/fpdfsdk/src/fpdfview_c_api_test.c b/fpdfsdk/src/fpdfview_c_api_test.c
index a17f7b6c1e82666bb2aeaf925bbf6ace45c7d16f..9bd2747f8375934233956f3c2e99b5d12b989ab2 100644
--- a/fpdfsdk/src/fpdfview_c_api_test.c
+++ b/fpdfsdk/src/fpdfview_c_api_test.c
@@ -54,6 +54,7 @@ int CheckPDFiumCApi() {
     CHK(FPDFAction_GetURIPath);
     CHK(FPDFDest_GetPageIndex);
     CHK(FPDFLink_GetLinkAtPoint);
+    CHK(FPDFLink_GetLinkZOrderAtPoint);
     CHK(FPDFLink_GetDest);
     CHK(FPDFLink_GetAction);
     CHK(FPDFLink_Enumerate);
@@ -106,7 +107,9 @@ int CheckPDFiumCApi() {
     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);