Add dropdown demo page for implementation testing

src/Connected.Components.Showcase.Runner/Pages/DropdownDemo.razor

@@ -0,0 +1,18 @@
+@page "/demo/components/dropdown"
+
+@namespace Connected.Components.Showcase.Runner
+
+@using Connected.Components;
+
+<Dropdown Items=@Items ItemToKey=@((e) => e.Value.ToString()) @bind-SelectedItems="@SelectedItems" AllowMultiple=true>
+   <OptionTemplate>
+      @context.Name
+   </OptionTemplate>
+   <SelectedValueTemplate>
+      @context.Name
+   </SelectedValueTemplate>
+</Dropdown>
+
+<div>
+   @string.Join(", ", SelectedItems.Select(e=> e.Value))
+</div>

src/Connected.Components.Showcase.Runner/Pages/DropdownDemo.razor.cs

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+using System.Collections.ObjectModel;
+
+namespace Connected.Components.Showcase.Runner;
+
+public partial class DropdownDemo
+{
+	private ObservableCollection<TestObject> SelectedItems { get; set; } = new();
+
+	private ObservableCollection<TestObject> Items { get; set; } = new ObservableCollection<TestObject>
+	{
+		new TestObject
+		{
+			Name= "Simple",
+			Value = 1
+		},
+		new TestObject
+		{
+			Name = "Simpler",
+			Value = 2
+		}
+	};
+
+	public class TestObject
+	{
+		public string Name { get; set; }
+
+		public long Value { get; set; }
+	}
+}