Temporarily added MudBlazor.Markdown to the solution

This is necessary due to issue https://github.com/MyNihongo/MudBlazor.Markdown/issues/247

I created a PR as well: https://github.com/MyNihongo/MudBlazor.Markdown/pull/246

MudBlazor.Markdown/Models/HtmlDetailsData.cs

@@ -0,0 +1,14 @@
+namespace MudBlazor;
+
+internal readonly ref struct HtmlDetailsData
+{
+	public HtmlDetailsData(string header, string content)
+	{
+		Header = header;
+		Content = content;
+	}
+
+	public string Header { get; }
+
+	public string Content { get; }
+}

MudBlazor.Markdown/Models/StringLineGroupIndex.cs

@@ -0,0 +1,14 @@
+namespace MudBlazor;
+
+internal readonly ref struct StringLineGroupIndex
+{
+	public StringLineGroupIndex(int line, int index)
+	{
+		Line = line;
+		Index = index;
+	}
+
+	public int Line { get; }
+
+	public int Index { get; }
+}

MudBlazor.Markdown/Models/StringLineGroupRange.cs

@@ -0,0 +1,14 @@
+namespace MudBlazor;
+
+internal readonly ref struct StringLineGroupRange
+{
+	public StringLineGroupRange(StringLineGroupIndex start, StringLineGroupIndex end)
+	{
+		Start = start;
+		End = end;
+	}
+
+	public StringLineGroupIndex Start { get; }
+
+	public StringLineGroupIndex End { get; }
+}