Add global usings (#668)

* Use global usings

* Fix namespace declarations for test projects

src/Spectre.Console/Prompts/ConfirmationPrompt.cs

@@ -1,6 +1,3 @@
-using System.Threading;
-using System.Threading.Tasks;
-
 namespace Spectre.Console;
 
 /// <summary>

src/Spectre.Console/Prompts/IPrompt.cs

@@ -1,6 +1,3 @@
-using System.Threading;
-using System.Threading.Tasks;
-
 namespace Spectre.Console;
 
 /// <summary>

src/Spectre.Console/Prompts/List/IListPromptStrategy.cs

@@ -1,7 +1,3 @@
-using System;
-using System.Collections.Generic;
-using Spectre.Console.Rendering;
-
 namespace Spectre.Console;
 
 /// <summary>

src/Spectre.Console/Prompts/List/ListPrompt.cs

@@ -1,9 +1,3 @@
-using System;
-using System.Linq;
-using System.Threading;
-using System.Threading.Tasks;
-using Spectre.Console.Rendering;
-
 namespace Spectre.Console;
 
 internal sealed class ListPrompt<T>

src/Spectre.Console/Prompts/List/ListPromptItem.cs

@@ -1,5 +1,3 @@
-using System.Collections.Generic;
-
 namespace Spectre.Console;
 
 internal sealed class ListPromptItem<T> : IMultiSelectionItem<T>

src/Spectre.Console/Prompts/List/ListPromptRenderHook.cs

@@ -1,7 +1,3 @@
-using System;
-using System.Collections.Generic;
-using Spectre.Console.Rendering;
-
 namespace Spectre.Console;
 
 internal sealed class ListPromptRenderHook<T> : IRenderHook

src/Spectre.Console/Prompts/List/ListPromptState.cs

@@ -1,6 +1,3 @@
-using System;
-using System.Collections.Generic;
-
 namespace Spectre.Console;
 
 internal sealed class ListPromptState<T>

src/Spectre.Console/Prompts/List/ListPromptTree.cs

@@ -1,6 +1,3 @@
-using System;
-using System.Collections.Generic;
-
 namespace Spectre.Console;
 
 internal sealed class ListPromptTree<T>

src/Spectre.Console/Prompts/MultiSelectionPrompt.cs

@@ -1,11 +1,3 @@
-using System;
-using System.Collections.Generic;
-using System.ComponentModel;
-using System.Linq;
-using System.Threading;
-using System.Threading.Tasks;
-using Spectre.Console.Rendering;
-
 namespace Spectre.Console;
 
 /// <summary>

src/Spectre.Console/Prompts/MultiSelectionPromptExtensions.cs

@@ -1,6 +1,3 @@
-using System;
-using System.Collections.Generic;
-
 namespace Spectre.Console;
 
 /// <summary>

src/Spectre.Console/Prompts/SelectionPrompt.cs

@@ -1,10 +1,3 @@
-using System;
-using System.Collections.Generic;
-using System.ComponentModel;
-using System.Threading;
-using System.Threading.Tasks;
-using Spectre.Console.Rendering;
-
 namespace Spectre.Console;
 
 /// <summary>

src/Spectre.Console/Prompts/SelectionPromptExtensions.cs

@@ -1,6 +1,3 @@
-using System;
-using System.Collections.Generic;
-
 namespace Spectre.Console;
 
 /// <summary>

src/Spectre.Console/Prompts/TextPrompt.cs

@@ -1,13 +1,3 @@
-using System;
-using System.Collections.Generic;
-using System.ComponentModel;
-using System.Diagnostics.CodeAnalysis;
-using System.Globalization;
-using System.Linq;
-using System.Text;
-using System.Threading;
-using System.Threading.Tasks;
-
 namespace Spectre.Console;
 
 /// <summary>

src/Spectre.Console/Prompts/TextPromptExtensions.cs

@@ -1,6 +1,3 @@
-using System;
-using System.Collections.Generic;
-
 namespace Spectre.Console;
 
 /// <summary>