(AB-161630) Refactor and extend class docs

Prior to this change, the class documentation did not go into sufficient
detail for the syntax, definition, and limitations of class members.

This change decomposes the `about_Classes` documentation into multiple
files:

- `about_Classes` - overview, basic information, full list of limitations.
- `about_Classes_Properties` - Full documentation for defining class
  properties.
- `about_Classes_Methods` - Full documentation for defining class methods.
- `about_Classes_Constructors` - Full documentation for defining class
  constructors.
- `about_Classes_Inheritance` - Full documentation for defining classes
  that inherit from a base class or implement an interface.

This change fixes AB#161630.

reference/7.3/Microsoft.PowerShell.Core/About/About.md

@@ -2,7 +2,7 @@
 description: About topics cover a range of concepts about PowerShell.
 Help Version: 7.2.0.0
 Locale: en-US
-ms.date: 03/18/2022
+ms.date: 11/07/2023
 title: About topics
 ---
 # About topics
@@ -61,6 +61,18 @@ Describes a **CimSession** object and the difference between CIM sessions and Po
 ### [about_Classes](about_Classes.md)
 Describes how you can use classes to create your own custom types.
 
+### [about_Classes_Constructors](about_Classes_Constructors.md)
+Describes how to define constructors for PowerShell classes.
+
+### [about_Classes_Inheritance](about_Classes_Inheritance.md)
+Describes how you can define classes that extend other types.
+
+### [about_Classes_Methods](about_Classes_Methods.md)
+Describes how to define methods for PowerShell classes.
+
+### [about_Classes_Properties](about_Classes_Properties.md)
+Describes how to define properties for PowerShell classes.
+
 ### [about_Command_Precedence](about_Command_Precedence.md)
 Describes how PowerShell determines which command to run.