Add getStateSummary method for diagnostics

Summary:
Adds a more structured representation of state updates than a multiline string.
Also changes the string form to omit [started] records.

Reviewed By: danielbuechele

Differential Revision: D9315503

fbshipit-source-id: 55b8f9572091fd42fe852c8d26a8f2a53f76c82a

xplat/Sonar/SonarClient.h

@@ -16,6 +16,7 @@
 #include <map>
 #include <mutex>
 #include "SonarStep.h"
+#include <vector>
 
 namespace facebook {
 namespace sonar {
@@ -77,6 +78,8 @@ class SonarClient : public SonarWebSocket::Callbacks {
 
   std::string getState();
 
+  std::vector<StateElement> getStateElements();
+
   template <typename P>
   std::shared_ptr<P> getPlugin(const std::string& identifier) {
     return std::static_pointer_cast<P>(getPlugin(identifier));