Revert expected event handler names for AV1738

Because a fix for https://youtrack.jetbrains.com/issue/RSRP-461586 is
still not in place, this matches the current Resharper behavior.

Author: Bart Koelman

docs/Overview.md

@@ -102,7 +102,7 @@ The list below describes per rule what its analyzer reports on. Checked rules ar
 - [x] This analyzer reports public and internal boolean parameters and members whose names do not start with words like "Is", "Has", "Can" etc.
 
 ### [AV1738](https://github.com/dennisdoomen/CSharpGuidelines/blob/master/Src/Guidelines/1700_NamingGuidelines.md#av1738): Prefix an event handler with On (LOW)
-- [x] This analyzer reports when the target method in an event handler assignment does not match the pattern "On" followed by target field name and the name of the event.
+- [x] This analyzer reports when the target method in an event handler assignment does not match the pattern: target field name, followed by "On" and the name of the event.
 
 ### [AV1739](https://github.com/dennisdoomen/CSharpGuidelines/blob/master/Src/Guidelines/1700_NamingGuidelines.md#av1739): Use an underscore for irrelevant lambda parameters (LOW)
 - [x] This analyzer reports unused lambda parameters whose names contain any characters other than underscores.

src/CSharpGuidelinesAnalyzer/CSharpGuidelinesAnalyzer.Test/Specs/Naming/PrefixEventHandlersWithOnSpecs.cs

@@ -138,10 +138,10 @@ public class C
 
                         public void M()
                         {
-                            _topLeft.ValueChanged += OnTopLeftValueChanged;
+                            _topLeft.ValueChanged += TopLeftOnValueChanged;
                         }
 
-                        public void OnTopLeftValueChanged(object sender, EventArgs e)
+                        public void TopLeftOnValueChanged(object sender, EventArgs e)
                         {
                         }
                     }
@@ -181,7 +181,7 @@ public void HandleTopLeftValueChanged(object sender, EventArgs e)
 
             // Act and assert
             VerifyGuidelineDiagnostic(source,
-                "Method 'HandleTopLeftValueChanged' that handles event 'ValueChanged' should be renamed to 'OnTopLeftValueChanged'.");
+                "Method 'HandleTopLeftValueChanged' that handles event 'ValueChanged' should be renamed to 'TopLeftOnValueChanged'.");
         }
 
         [Fact]

src/CSharpGuidelinesAnalyzer/CSharpGuidelinesAnalyzer/Rules/Naming/PrefixEventHandlersWithOnAnalyzer.cs

@@ -54,7 +54,7 @@ private static void AnalyzeEventAssignmentMethod([NotNull] IMethodBindingExpress
             [NotNull] IEventAssignmentExpression assignment, OperationAnalysisContext context)
         {
             string eventTargetName = GetEventTargetName(assignment.EventInstance);
-            string handlerNameExpected = string.Concat("On", eventTargetName, assignment.Event.Name);
+            string handlerNameExpected = string.Concat(eventTargetName, "On", assignment.Event.Name);
 
             string handlerNameActual = binding.Method.Name;
             if (handlerNameActual != handlerNameExpected)