Add chapter 12 blazor project

Chapter12/Complete/BlazorTasksWasm/Pages/Counter.razor

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+@page "/counter"
+
+<PageTitle>Counter</PageTitle>
+
+<h1>Counter</h1>
+
+<p role="status">Current count: @currentCount</p>
+
+<button class="btn btn-primary" @onclick="IncrementCount">Click me</button>
+
+@code {
+    private int currentCount = 0;
+
+    private void IncrementCount()
+    {
+        currentCount++;
+    }
+}