C26874: replacing Markdon Italics by HTML Italic tags (#6352)

Hello, @mairaw ,
Localization team has reported source content issue that causes localized version to have broken/different format compared to en-us version.  
"Italics should be replaced with HTML tags <em></em> to avoid broken content on localization"
 
Please review and merge the proposed file change to fix to target versions. If you make related fix in another PR  then share your PR number so we can confirm and close this PR.

Many thanks in advance.

Author: v-maudel

docs/standard/asynchronous-programming-patterns/best-practices-for-implementing-the-event-based-asynchronous-pattern.md

@@ -22,14 +22,14 @@ The Event-based Asynchronous Pattern provides you with an effective way to expos
  If you implement the Event-based Asynchronous Pattern, you must provide a number of guarantees to ensure that your class will behave properly and clients of your class can rely on such behavior.  
 
 ### Completion  
- Always invoke the *MethodName***Completed** event handler when you have successful completion, an error, or a cancellation. Applications should never encounter a situation where they remain idle and completion never occurs. One exception to this rule is if the asynchronous operation itself it designed so that it never completes.  
+ Always invoke the <em>MethodName</em>**Completed** event handler when you have successful completion, an error, or a cancellation. Applications should never encounter a situation where they remain idle and completion never occurs. One exception to this rule is if the asynchronous operation itself it designed so that it never completes.  
 
 ### Completed Event and EventArgs  
- For each separate *MethodName***Async** method, apply the following design requirements:  
+ For each separate <em>MethodName</em>**Async** method, apply the following design requirements:  
 
--   Define a *MethodName***Completed** event on the same class as the method.  
+-   Define a <em>MethodName</em>**Completed** event on the same class as the method.  
 
--   Define an <xref:System.EventArgs> class and accompanying delegate for the *MethodName***Completed** event that derives from the <xref:System.ComponentModel.AsyncCompletedEventArgs> class. The default class name should be of the form *MethodName***CompletedEventArgs**.  
+-   Define an <xref:System.EventArgs> class and accompanying delegate for the <em>MethodName</em>**Completed** event that derives from the <xref:System.ComponentModel.AsyncCompletedEventArgs> class. The default class name should be of the form *MethodName***CompletedEventArgs**.  
 
 -   Ensure that the <xref:System.EventArgs> class is specific to the return values of the *MethodName* method. When you use the <xref:System.EventArgs> class, you should never require developers to cast the result.