Improve MetricEventSource error message (#55319)

The Error event wasn't capturing inner exception info
in its message. Switching from Exception.Message to
Exception.ToString() captures more useful messages.
We no longer split out the stack separately, but that
wasn't important. The error messages are likely only
useful for humans anyway.

src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Metrics/MetricsEventSource.cs

@@ -138,9 +138,9 @@ public void EndInstrumentReporting(string sessionId, string meterName, string? m
         }
 
         [Event(9, Keywords = Keywords.TimeSeriesValues | Keywords.Messages | Keywords.InstrumentPublishing)]
-        public void Error(string sessionId, string errorMessage, string errorStack)
+        public void Error(string sessionId, string errorMessage)
         {
-            WriteEvent(9, sessionId, errorMessage, errorStack);
+            WriteEvent(9, sessionId, errorMessage);
         }
 
         [Event(10, Keywords = Keywords.TimeSeriesValues | Keywords.InstrumentPublishing)]
@@ -203,7 +203,7 @@ public void OnEventCommand(EventCommandEventArgs command)
                         // This limitation shouldn't really matter because browser also doesn't support out-of-proc EventSource communication
                         // which is the intended scenario for this EventSource. If it matters in the future AggregationManager can be
                         // modified to have some other fallback path that works for browser.
-                        Log.Error("", "System.Diagnostics.Metrics EventSource not supported on browser", "");
+                        Log.Error("", "System.Diagnostics.Metrics EventSource not supported on browser");
                         return;
                     }
 #endif
@@ -301,7 +301,7 @@ public void OnEventCommand(EventCommandEventArgs command)
                             i => Log.EndInstrumentReporting(sessionId, i.Meter.Name, i.Meter.Version, i.Name, i.GetType().Name, i.Unit, i.Description),
                             i => Log.InstrumentPublished(sessionId, i.Meter.Name, i.Meter.Version, i.Name, i.GetType().Name, i.Unit, i.Description),
                             () => Log.InitialInstrumentEnumerationComplete(sessionId),
-                            e => Log.Error(sessionId, e.Message, e.StackTrace?.ToString() ?? ""),
+                            e => Log.Error(sessionId, e.ToString()),
                             () => Log.TimeSeriesLimitReached(sessionId),
                             () => Log.HistogramLimitReached(sessionId));
 
@@ -328,7 +328,7 @@ public void OnEventCommand(EventCommandEventArgs command)
 
             private bool LogError(Exception e)
             {
-                Log.Error(_sessionId, e.Message, e.StackTrace?.ToString() ?? "");
+                Log.Error(_sessionId, e.ToString());
                 // this code runs as an exception filter
                 // returning false ensures the catch handler isn't run
                 return false;

src/libraries/System.Diagnostics.DiagnosticSource/tests/MetricEventSourceTests.cs

@@ -1001,8 +1001,7 @@ private void AssertOnError()
                 if (errorEvent != null)
                 {
                     string message = errorEvent.Payload[1].ToString();
-                    string stackTrace = errorEvent.Payload[2].ToString();
-                    Assert.True(errorEvent == null, "Unexpected Error event: " + message + Environment.NewLine + stackTrace);
+                    Assert.True(errorEvent == null, "Unexpected Error event: " + message);
                 }
             }
         }