fix: remove all build warnings

[JohnTasler]

This cleans up all warnings that are generated when building Wpf.Ui.sln.

Pull request type

• Build related changes

What is the current behavior?

Issue Numbers: #1332 and #1333

What is the new behavior?

No warnings are generated when building.

Other information

This PR closes #1332. Also closes #1333.

[JohnTasler]

A couple of notes:

1. On the TitleBar control, the analyzer said that the return value for Header and TrailingContent properties should be a object? rather than object. My concern is that since these are public properties, it might cause a breaking change for someone.
2. The documentation for warning CA1060 says "Do not suppress a warning from this rule.". However, I did exactly that. I can think of some other ways, but they seem to be a lot of effort that may not be worth it. The easiest way would be to make the current static classes namespaces instead of classes, and then in those namespaces, to rename the class to NativeMethods. For example:

namespace Wpf.Ui.Interop.Shell32;

/// <summary>
/// The Windows UI provides users with access to a wide variety of objects necessary to run applications and manage the operating system.
/// </summary>
internal static class NativeMethods
{

This would require several code changes at all the call sites. However, these could be reduced using this syntax at the top of each file using the interop methods.

using Shell32 = Wpf.Ui.Interop.Shell32.NativeMethods;

Let me know how you want to proceed. Disable the warning as I have done here, or go through and fix all of them.

[pomianowski]

Hey @JohnTasler, thanks for another PR and fixes to the library. Great that you also updated the packages. Changing object? to object was probably an accident, this value could potentially be null i think, so as a regression I would change it in 4.0.1 to object?.

As for the interop warning, I would think about it in another PR, I created a separate issue where it can be discussed #1338