Implement SetStats for TGraph. (#8498)

As requested here: https://root-forum.cern.ch/t/remove-stats-box-from-fitted-tgraph/45490

README/ReleaseNotes/v626/index.md

@@ -63,6 +63,8 @@ The following people have contributed to this new version:
 
 ## Histogram Libraries
 
+- Implement the `SetStats` method for `TGraph` to turn ON or OFF the statistics box display
+  for an individual `TGraph`.
 
 ## Math Libraries
 

hist/hist/inc/TGraph.h

@@ -67,6 +67,7 @@ class TGraph : public TNamed, public TAttLine, public TAttFill, public TAttMarke
 public:
    // TGraph status bits
    enum EStatusBits {
+      kNoStats       = BIT(9),   ///< Don't draw stats box
       kClipFrame     = BIT(10),  ///< Clip to the frame boundary
       kResetHisto    = BIT(17),  ///< fHistogram must be reset in GetHistogram
       kNotEditable   = BIT(18),  ///< Bit set if graph is non editable
@@ -182,6 +183,7 @@ class TGraph : public TNamed, public TAttLine, public TAttFill, public TAttMarke
    virtual void          SetPointY(Int_t i, Double_t y);
    virtual void          SetName(const char *name=""); // *MENU*
    virtual void          SetNameTitle(const char *name="", const char *title="");
+   virtual void          SetStats(Bool_t stats=kTRUE); // *MENU*
    virtual void          SetTitle(const char *title="");    // *MENU*
    virtual void          Sort(Bool_t (*greater)(const TGraph*, Int_t, Int_t)=&TGraph::CompareX,
                               Bool_t ascending=kTRUE, Int_t low=0, Int_t high=-1111);

hist/hist/src/TGraph.cxx

@@ -2362,6 +2362,30 @@ void TGraph::SetNameTitle(const char *name, const char *title)
    SetTitle(title);
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// Set statistics option on/off.
+///
+/// By default, the statistics box is drawn.
+/// The paint options can be selected via gStyle->SetOptStats.
+/// This function sets/resets the kNoStats bit in the graph object.
+/// It has priority over the Style option.
+
+void TGraph::SetStats(Bool_t stats)
+{
+   ResetBit(kNoStats);
+   if (!stats) {
+      SetBit(kNoStats);
+      //remove the "stats" object from the list of functions
+      if (fFunctions) {
+         TObject *obj = fFunctions->FindObject("stats");
+         if (obj) {
+            fFunctions->Remove(obj);
+            delete obj;
+         }
+      }
+   }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 /// if size*2 <= fMaxSize allocate new arrays of size points,
 /// copy points [0,oend).

hist/histpainter/src/TGraphPainter.cxx

@@ -1268,7 +1268,7 @@ void TGraphPainter::PaintHelper(TGraph *theGraph, Option_t *option)
             }
          }
       }
-      if (fit) PaintStats(theGraph, fit);
+      if (fit && !theGraph->TestBit(TGraph::kNoStats)) PaintStats(theGraph, fit);
 
    }
 }