Move solution and projects to src

src/Ryujinx.Ava/App.axaml

@@ -0,0 +1,9 @@
+<Application
+    x:Class="Ryujinx.Ava.App"
+    xmlns="https://github.com/avaloniaui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:sty="using:FluentAvalonia.Styling">
+    <Application.Styles>
+        <sty:FluentAvaloniaTheme PreferSystemTheme="False" />
+    </Application.Styles>
+</Application>