Add docs for EventCounter.Dispose() and DiagnosticsListener.IsEnabled (#3235)

* Add docs for EventCounter.Dispose() and DiagnosticsListener.IsEnabled

* Update xml/System.Diagnostics/DiagnosticListener.xml

Co-Authored-By: Carlos Sanchez Lopez <[email protected]>

* spacing + cref to EventSource

* Update xml/System.Diagnostics/DiagnosticListener.xml

Co-Authored-By: Noah Falk <[email protected]>

* Update xml/System.Diagnostics.Tracing/EventCounter.xml

Co-Authored-By: Noah Falk <[email protected]>

* Update xml/System.Diagnostics/DiagnosticListener.xml

Co-Authored-By: Noah Falk <[email protected]>

* address suggestions by carlossanlop

* Point the see cref to the member group without %2A

* suggestion by gewarren (Overload)

Author: sywhang

xml/System.Diagnostics.Tracing/EventCounter.xml

@@ -109,8 +109,16 @@ For an example of how to use the <xref:System.Diagnostics.Tracing.EventCounter>
       </ReturnValue>
       <Parameters />
       <Docs>
-        <summary>Releases the resources used by the current instance of the <see cref="T:System.Diagnostics.Tracing.EventCounter" /> class.</summary>
-        <remarks>To be added.</remarks>
+        <summary>Removes the counter from the set that the <see cref="T:System.Diagnostics.Tracing.EventSource" /> will report on.</summary>
+        <remarks>
+          <format type="text/markdown"><![CDATA[
+
+## Remarks
+
+After being disposed, this counter will stop reporting values. If an <xref:System.Diagnostics.Tracing.EventCounter> is not explicitly disposed it will stop reporting automatically when the <xref:System.Diagnostics.Tracing.EventSource> it is attached to is disposed.
+
+          ]]></format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName="ToString">

xml/System.Diagnostics/DiagnosticListener.xml

@@ -213,10 +213,10 @@ If setup for the notification is expensive, you can call `IsEnabled()` before pe
         <Parameter Name="arg2" Type="System.Object" Index="2" FrameworkAlternate="netcore-2.0;netcore-2.1;netcore-2.2;netcore-3.0" />
       </Parameters>
       <Docs>
-        <param name="name">To be added.</param>
-        <param name="arg1">To be added.</param>
-        <param name="arg2">To be added.</param>
-        <summary>Checks if the DiagnosticListener is enabled.</summary>
+        <param name="name">The name of the event to check.</param>
+        <param name="arg1">The object that represents a context.</param>
+        <param name="arg2">The object that represents a context.</param>
+        <summary>Checks if any subscriber to the diagnostic events is interested in receiving events with this name. Subscribers indicate their interest using a delegate provided in <see cref="Overload:System.Diagnostics.DiagnosticListener.Subscribe" />.</summary>
         <returns>
           <see langword="true" /> if it is enabled, <see langword="false" /> otherwise.</returns>
         <remarks>To be added.</remarks>
@@ -298,6 +298,18 @@ If setup for the notification is expensive, you can call `IsEnabled()` before pe
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
+    <MemberGroup MemberName="Subscribe">
+      <AssemblyInfo>
+        <AssemblyName>System.Diagnostics.DiagnosticSource</AssemblyName>
+        <AssemblyVersion>4.0.2.0</AssemblyVersion>
+        <AssemblyVersion>4.0.2.1</AssemblyVersion>
+        <AssemblyVersion>4.0.3.0</AssemblyVersion>
+        <AssemblyVersion>4.0.4.0</AssemblyVersion>
+      </AssemblyInfo>
+      <Docs>
+        <summary>These methods allow adding a subscriber, and some of them provide optional event filtering methods.</summary>
+      </Docs>
+    </MemberGroup>
     <Member MemberName="Subscribe">
       <MemberSignature Language="C#" Value="public IDisposable Subscribe (IObserver&lt;System.Collections.Generic.KeyValuePair&lt;string,object&gt;&gt; observer);" FrameworkAlternate="netcore-1.0;netcore-1.1" />
       <MemberSignature Language="ILAsm" Value=".method public hidebysig newslot virtual instance class System.IDisposable Subscribe(class System.IObserver`1&lt;valuetype System.Collections.Generic.KeyValuePair`2&lt;string, object&gt;&gt; observer) cil managed" />