Added mono solution platform.

And removed the projects that don't apply/dont build on mono from it.

samples/BindingTest/BindingTest.csproj

@@ -153,11 +153,11 @@
       <Project>{3e10a5fa-e8da-48b1-ad44-6a5b6cb7750f}</Project>
       <Name>Avalonia.Themes.Default</Name>
     </ProjectReference>
-    <ProjectReference Include="..\..\src\Windows\Avalonia.Direct2D1\Avalonia.Direct2D1.csproj">
+    <ProjectReference Include="..\..\src\Windows\Avalonia.Direct2D1\Avalonia.Direct2D1.csproj" Condition="'$(Platform)'!='Mono'">
       <Project>{3e908f67-5543-4879-a1dc-08eace79b3cd}</Project>
       <Name>Avalonia.Direct2D1</Name>
     </ProjectReference>
-    <ProjectReference Include="..\..\src\Windows\Avalonia.Win32\Avalonia.Win32.csproj">
+    <ProjectReference Include="..\..\src\Windows\Avalonia.Win32\Avalonia.Win32.csproj" Condition="'$(Platform)'!='Mono'">
       <Project>{811a76cf-1cf6-440f-963b-bbe31bd72a82}</Project>
       <Name>Avalonia.Win32</Name>
     </ProjectReference>

samples/ControlCatalog.Desktop/ControlCatalog.Desktop.csproj

@@ -119,15 +119,15 @@
       <Project>{3E10A5FA-E8DA-48B1-AD44-6A5B6CB7750F}</Project>
       <Name>Avalonia.Themes.Default</Name>
     </ProjectReference>
-    <ProjectReference Include="..\..\src\Skia\Avalonia.Skia.Desktop\Avalonia.Skia.Desktop.csproj">
+    <ProjectReference Include="..\..\src\Skia\Avalonia.Skia.Desktop\Avalonia.Skia.Desktop.csproj" Condition="'$(Platform)'!='Mono'">
       <Project>{925DD807-B651-475F-9F7C-CBEB974CE43D}</Project>
       <Name>Avalonia.Skia.Desktop</Name>
     </ProjectReference>
-    <ProjectReference Include="..\..\src\Windows\Avalonia.Direct2D1\Avalonia.Direct2D1.csproj">
+    <ProjectReference Include="..\..\src\Windows\Avalonia.Direct2D1\Avalonia.Direct2D1.csproj" Condition="'$(Platform)'!='Mono'">
       <Project>{3E908F67-5543-4879-A1DC-08EACE79B3CD}</Project>
       <Name>Avalonia.Direct2D1</Name>
     </ProjectReference>
-    <ProjectReference Include="..\..\src\Windows\Avalonia.Win32\Avalonia.Win32.csproj">
+    <ProjectReference Include="..\..\src\Windows\Avalonia.Win32\Avalonia.Win32.csproj" Condition="'$(Platform)'!='Mono'">
       <Project>{811A76CF-1CF6-440F-963B-BBE31BD72A82}</Project>
       <Name>Avalonia.Win32</Name>
     </ProjectReference>

samples/TestApplication/TestApplication.csproj

@@ -151,11 +151,11 @@
       <Project>{3E10A5FA-E8DA-48B1-AD44-6A5B6CB7750F}</Project>
       <Name>Avalonia.Themes.Default</Name>
     </ProjectReference>
-    <ProjectReference Include="..\..\src\Windows\Avalonia.Direct2D1\Avalonia.Direct2D1.csproj">
+    <ProjectReference Include="..\..\src\Windows\Avalonia.Direct2D1\Avalonia.Direct2D1.csproj" Condition="'$(Platform)'!='Mono'">
       <Project>{3E908F67-5543-4879-A1DC-08EACE79B3CD}</Project>
       <Name>Avalonia.Direct2D1</Name>
     </ProjectReference>
-    <ProjectReference Include="..\..\src\Windows\Avalonia.Win32\Avalonia.Win32.csproj">
+    <ProjectReference Include="..\..\src\Windows\Avalonia.Win32\Avalonia.Win32.csproj" Condition="'$(Platform)'!='Mono'">
       <Project>{811A76CF-1CF6-440F-963B-BBE31BD72A82}</Project>
       <Name>Avalonia.Win32</Name>
     </ProjectReference>

samples/VirtualizationTest/VirtualizationTest.csproj

@@ -142,11 +142,11 @@
       <Project>{6417e941-21bc-467b-a771-0de389353ce6}</Project>
       <Name>Avalonia.Markup</Name>
     </ProjectReference>
-    <ProjectReference Include="..\..\src\Windows\Avalonia.Direct2D1\Avalonia.Direct2D1.csproj">
+    <ProjectReference Include="..\..\src\Windows\Avalonia.Direct2D1\Avalonia.Direct2D1.csproj" Condition="'$(Platform)'!='Mono'">
       <Project>{3e908f67-5543-4879-a1dc-08eace79b3cd}</Project>
       <Name>Avalonia.Direct2D1</Name>
     </ProjectReference>
-    <ProjectReference Include="..\..\src\Windows\Avalonia.Win32\Avalonia.Win32.csproj">
+    <ProjectReference Include="..\..\src\Windows\Avalonia.Win32\Avalonia.Win32.csproj" Condition="'$(Platform)'!='Mono'">
       <Project>{811a76cf-1cf6-440f-963b-bbe31bd72a82}</Project>
       <Name>Avalonia.Win32</Name>
     </ProjectReference>

samples/XamlTestApplication/XamlTestApplication.csproj

@@ -155,11 +155,11 @@
       <Project>{3E53A01A-B331-47F3-B828-4A5717E77A24}</Project>
       <Name>Avalonia.Markup.Xaml</Name>
     </ProjectReference>
-    <ProjectReference Include="..\..\src\Windows\Avalonia.Direct2D1\Avalonia.Direct2D1.csproj">
+    <ProjectReference Include="..\..\src\Windows\Avalonia.Direct2D1\Avalonia.Direct2D1.csproj" Condition="'$(Platform)'!='Mono'">
       <Project>{3E908F67-5543-4879-A1DC-08EACE79B3CD}</Project>
       <Name>Avalonia.Direct2D1</Name>
     </ProjectReference>
-    <ProjectReference Include="..\..\src\Windows\Avalonia.Win32\Avalonia.Win32.csproj">
+    <ProjectReference Include="..\..\src\Windows\Avalonia.Win32\Avalonia.Win32.csproj" Condition="'$(Platform)'!='Mono'">
       <Project>{811A76CF-1CF6-440F-963B-BBE31BD72A82}</Project>
       <Name>Avalonia.Win32</Name>
     </ProjectReference>