Survey JSON performance warning for non-wre-standard JSON modules/versions

If you have funny combinations of JSON, JSON::XS and JSON::PP installed,
JSON can start deciding to use JSON::PP instead of JSON::XS, which equals
bad performance on very large Survey instances.

This commit adds a new warning to the Edit Survey page if JSON->backend
is detected to be something other than JSON::XS.

docs/changelog/7.x.x.txt

@@ -37,6 +37,7 @@
  - fixed Survey ExpireIncompleteSurveyResponses Workflow Activity not enabled (Patrick Donelan, SDH Consulting)
  - fixed #10689: Version Tag Modes (Henry Tang, Long Term Results B.V.)
  - fixed #10733: viewing pending version tags
+ - added Survey JSON performance warning for people with non-wre-standard JSON modules/versions (Patrick Donelan, SDH Consulting)
 
 7.7.16
  - fixed #10590: Session::DateTime->secondsToInterval doesn't allow 7 weeks

lib/WebGUI/Asset/Wobject/Survey/SurveyJSON.pm

@@ -1370,7 +1370,10 @@ Returns an array of messages to inform a user what is logically wrong with the S
 sub validateSurvey{
     my $self = shift;
 
-    my @messages;   
+    my @messages;
+    if (JSON->backend ne 'JSON::XS') {
+        push @messages, "Your server is using @{[JSON->backend]} as its JSON backend. This may hurt performance on large Survey instances";
+    }
 
     #set up valid goto targets 
     my $gotoTargets = $self->getGotoTargets();