Should mention differentiation between property schema changes and item data changes

The constructor with a propertychanged mentions that it should only be used for object schema changes and with adequate `ListChangedType` value.

This is in contrast to item changes, which specify item indices and different `ListChangedType` values.

The remarks section on this type, `ListChangedEventArgs`, should mention and describe this differentiation.

Furthermore, it is unclear how a combination of the two should be handled. The `ListChangedType` can not be combined, but constructors with both types of parameters imply this is somehow possible and intended, but they do not document how it's supposed to work/be handled.

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#### Document Details

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* ID: 97c8c9f6-72f6-2fb9-feed-d9a0bfb6348f
* Version Independent ID: 72c6439d-375b-e584-fd70-593411554e41
* Content: [ListChangedEventArgs Class (System.ComponentModel)](https://docs.microsoft.com/en-us/dotnet/api/system.componentmodel.listchangedeventargs?view=netframework-4.7.2)
* Content Source: [xml/System.ComponentModel/ListChangedEventArgs.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.ComponentModel/ListChangedEventArgs.xml)
* Product: **dotnet-api**
* GitHub Login: @dotnet-bot
* Microsoft Alias: **dotnetcontent**

Start with xml/System.ComponentModel/ListChangedEventArgs.xml and its constructors and remarks, then review the referenced ListChangedType documentation to establish the distinction between property-schema and item-data changes. Done means the remarks clearly explain both cases and how constructor arguments should be handled together.

Written by the indexing model from the issue text.