Add `GlobalUsings.cs` to remove complexity of using different namespaces for WinUI2/3

[mrlacey]

Rather than have something like the following at the top of each file, it will be simpler and easier to specify these at a global level.

#if !WINAPPSDK
using Microsoft.Toolkit.Uwp;
using Microsoft.Toolkit.Uwp.UI;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Markup;
#else
using CommunityToolkit.WinUI;
using CommunityToolkit.WinUI.UI;
using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Controls;
using Microsoft.UI.Xaml.Markup;
#endif

This will also make it easier when adding new files to an experiment as it won't be necessary to add the above (or a variation thereof)

[michael-hawker]

Looking at the new GitHub search tool, in the 100 listings it gave me, roughly 2/3rds were GlobalUsings.cs compared to about 1/3rd Usings.cs. I did like someone's suggestion of starting the file with an underscore to list it first though to keep it present.

Thoughts on _GlobalUsings_.cs?

Also would we use one file across an experiment that's shared by the library, samples, and tests? Or would each project have its own copy? (I don't think we want one across the entire repo as that could get messy.)

[mrlacey]

Thoughts on _GlobalUsings_.cs?

I'm torn. I like the idea but also think it has the potential to be confusing as I've seen no evidence of widespread use.
As this will be added by a props file that points to the file in the common directory I don't think we need to give it a special name--most people will never see it.

Also would we use one file across an experiment that's shared by the library, samples, and tests? Or would each project have its own copy? (I don't think we want one across the entire repo as that could get messy.)

Before digging into this, at the very least we'll need a separate one for tests.
This will bring up a different set of naming questions.... GlobalUsings_Labs.cs GlobalUsings_Tests.cs ..?

[michael-hawker]

Before digging into this, at the very least we'll need a separate one for tests. This will bring up a different set of naming questions.... GlobalUsings_Labs.cs GlobalUsings_Tests.cs ..?

Right, I guess that comes to the question on if this is just housed by each project individually (library, samples, tests), so then they can all share the name and be in different directories.

vs.

Having central copies which try and cover all cases and are auto-included.

I would think having some control at the project layer would be important as if a project includes another dependency which may have separate namespaces, they may want to use the same technique. Though I suppose they can also just create their own global file within the project at that point too...