Add FPDFDest_GetLocationInPage API

Add an API to get the value of the /XYZ destination parameter.

This CL was originally from https://codereview.chromium.org/1960193003/ by
halcanary@.

Review-Url: https://codereview.chromium.org/2481743004
diff --git a/fpdfsdk/fpdfview_c_api_test.c b/fpdfsdk/fpdfview_c_api_test.c
index 4847180..a48ddb9 100644
--- a/fpdfsdk/fpdfview_c_api_test.c
+++ b/fpdfsdk/fpdfview_c_api_test.c
@@ -54,6 +54,7 @@
     CHK(FPDFAction_GetFilePath);
     CHK(FPDFAction_GetURIPath);
     CHK(FPDFDest_GetPageIndex);
+    CHK(FPDFDest_GetLocationInPage);
     CHK(FPDFLink_GetLinkAtPoint);
     CHK(FPDFLink_GetLinkZOrderAtPoint);
     CHK(FPDFLink_GetDest);