Update ValueTask`1.xml (#2073)

* Update ValueTask`1.xml

There is a non-generic version of ValueTask. The documentation was misleading.

* Update ValueTask`1.xml

Added suggested alternative.

* add brackets around xref

Once the build finishes, I'll merge it.

Author: baj22

xml/System.Threading.Tasks/ValueTask`1.xml

@@ -50,7 +50,7 @@ There are tradeoffs to using a <xref:System.Threading.Tasks.ValueTask%601> inste
 
 For uses other than consuming the result of an asynchronous operation using await, <xref:System.Threading.Tasks.ValueTask%601> can lead to a more convoluted programming model that requires more allocations. For example, consider a method that could return either a <xref:System.Threading.Tasks.Task%601> with a cached task as a common result or a <xref:System.Threading.Tasks.ValueTask%601>. If the consumer of the result wants to use it as a <xref:System.Threading.Tasks.Task%601> in a method like <xref:System.Threading.Tasks.Task.WhenAll%2A> or <xref:System.Threading.Tasks.Task.WhenAny%2A>, the <xref:System.Threading.Tasks.ValueTask%601> must first be converted to a <xref:System.Threading.Tasks.Task%601> using <xref:System.Threading.Tasks.ValueTask%601.AsTask%2A>, leading to an allocation that would have been avoided if a cached <xref:System.Threading.Tasks.Task%601> had been used in the first place.   
 
-As such, the default choice for any asynchronous method should be to return a <xref:System.Threading.Tasks.Task> or <xref:System.Threading.Tasks.Task%601>. Only if performance analysis proves it worthwhile should a <xref:System.Threading.Tasks.ValueTask%601> be used instead of a <xref:System.Threading.Tasks.Task%601>. There is no non-generic version of <xref:System.Threading.Tasks.ValueTask%601>, as the <xref:System.Threading.Tasks.Task.CompletedTask> property may be used to hand back a successfully completed singleton in the case where a method returning a <xref:System.Threading.Tasks.Task> completes synchronously and successfully.   
+As such, the default choice for any asynchronous method should be to return a <xref:System.Threading.Tasks.Task> or <xref:System.Threading.Tasks.Task%601>. Only if performance analysis proves it worthwhile should a <xref:System.Threading.Tasks.ValueTask%601> be used instead of a <xref:System.Threading.Tasks.Task%601>. The non generic version of <xref:System.Threading.Tasks.ValueTask> is not recommended for most scenarios. The <xref:System.Threading.Tasks.Task.CompletedTask> property should be used to hand back a successfully completed singleton in the case where a method returning a <xref:System.Threading.Tasks.Task> completes synchronously and successfully.
 
 > [!NOTE]
 >  The use of the <xref:System.Threading.Tasks.ValueTask%601> type is supported starting with C# 7.0, and is not supported by any version of Visual Basic.