For multi-tfm projects that contain a class with the designer attribute constantly set and resets the designer attribute

Reported here - https://developercommunity.visualstudio.com/content/problem/38882/project-that-targets-both-net46-and-netstandard15.html

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Version. Visual Studio 2017 RTM. All extensions disabled.
1. Start with an empty .NET Standard class library project. Edit the project file to so that it targets net46 and netstandard1.5 (e.g. net46;netstandard1.5) - this actually fails with any version of net and netstandard.
2. Add class that is a subclass of System.ComponentModel.Component. It can be as simple as this:
```csharp
#if NET46
using System.ComponentModel;
namespace ClassLibrary1
{
public class ComponentSubclass : Component
{
}
}
#endif
```
3. Observe that the project file is constantly changing. Visual Studio seems to be constantly adding/removing the following:
```xml


Component


```
As a result, the project and any other projects referencing this project are constantly recompiling.