Modernize C# FolderBrowserDialog example

[Varriount]

Update the C# example for the FolderBrowserDialog class to use MenuStrip, MenuStripItem, etc. classes instead of the deprecated MainMenu and MenuItem classes. Also make a few changes with regards to trailing spaces and formatting.

I left the names of all the variables, etc. the same so that it would differ too much from the other examples (and also because adding ToolStrip to the variable names wouldn't really justify the length increase).

[Varriount]

@dotnet-policy-service agree

[BillWagner]

Hi @Varriount

Can you address the suggestion I made? Once that's done, the build should complete successfully, and I'll merge this PR.

Also, in order for the CI build to pass, you need to add a .csproj file so the project builds. Since this is a desktop example, it will need a Visual Studio project, and a snippets.5000.json config file to specify Visual Studio as the build engine. There are several in this repo that you can copy to the project.

[learn-build-service-prod]

Learn Build status updates of commit 4a2e71b:

✅ Validation status: passed

File	Status	Preview URL	Details
snippets/csharp/System.Windows.Forms/FolderBrowserDialog/Overview/form1.cs	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[gewarren]

@Varriount Can you add the project file as well? Something like this one:

dotnet-api-docs/snippets/csharp/System.Windows.Forms/KeyPressEventArgs/Handled/Project.csproj

Line 6 in b09228a

<UseWindowsForms>true</UseWindowsForms>

(You don't need the snippets5000.json file that Bill mentioned.)

[learn-build-service-prod]

Learn Build status updates of commit 079f31e:

✅ Validation status: passed

File	Status	Preview URL	Details
snippets/csharp/System.Windows.Forms/FolderBrowserDialog/Overview/form1.cs	✅Succeeded	View
snippets/csharp/System.Windows.Forms/FolderBrowserDialog/Overview/Project.csproj	✅Succeeded

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel