Restructured CodeBehindGenerator pipeline (#20524)

* - Restructured CodeBehindGenerator pipeline to maximize SourceGen cachability
- Split out CSS SourceGen, which does not depend on Compilation at all
- Added TrackingNames to support new SourceGen unit test project

Fixes Issue #12978 CodeBehindGenerator has improper pipeline
Fixes AB#1947659: `CodeBehindGenerator` has improper pipeline

* - Use file-scoped namespaces throughout PR
- Use raw string literals for SourceGen tests

Microsoft.Maui-dev.sln

@@ -241,6 +241,10 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "UITest.Appium", "src\TestUt
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "UITest.NUnit", "src\TestUtils\src\UITest.NUnit\UITest.NUnit.csproj", "{A307B624-48D4-494E-A70D-5B3CDF6620CF}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Controls.SourceGen.UnitTests", "src\Controls\tests\SourceGen.UnitTests\Conrtrols.SourceGen.UnitTests\Controls.SourceGen.UnitTests.csproj", "{06747B55-91DB-47F5-B7A2-56526C28A0D3}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "SourceGen.UnitTests", "src\Controls\tests\SourceGen.UnitTests\SourceGen.UnitTests.csproj", "{BC7F7C82-694F-4B97-86FC-273FB3FACA25}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -610,6 +614,14 @@ Global
 		{A307B624-48D4-494E-A70D-5B3CDF6620CF}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{A307B624-48D4-494E-A70D-5B3CDF6620CF}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{A307B624-48D4-494E-A70D-5B3CDF6620CF}.Release|Any CPU.Build.0 = Release|Any CPU
+		{06747B55-91DB-47F5-B7A2-56526C28A0D3}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{06747B55-91DB-47F5-B7A2-56526C28A0D3}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{06747B55-91DB-47F5-B7A2-56526C28A0D3}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{06747B55-91DB-47F5-B7A2-56526C28A0D3}.Release|Any CPU.Build.0 = Release|Any CPU
+		{BC7F7C82-694F-4B97-86FC-273FB3FACA25}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{BC7F7C82-694F-4B97-86FC-273FB3FACA25}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{BC7F7C82-694F-4B97-86FC-273FB3FACA25}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{BC7F7C82-694F-4B97-86FC-273FB3FACA25}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -721,6 +733,8 @@ Global
 		{8F7B825D-24A8-4E09-AC5B-9117926B7BF3} = {7AC28763-9C68-4BF9-A1BA-25CBFFD2D15C}
 		{26379D0E-4D4D-48CA-94B1-A2C1972AB335} = {7AC28763-9C68-4BF9-A1BA-25CBFFD2D15C}
 		{A307B624-48D4-494E-A70D-5B3CDF6620CF} = {7AC28763-9C68-4BF9-A1BA-25CBFFD2D15C}
+		{06747B55-91DB-47F5-B7A2-56526C28A0D3} = {25D0D27A-C5FE-443D-8B65-D6C987F4A80E}
+		{BC7F7C82-694F-4B97-86FC-273FB3FACA25} = {25D0D27A-C5FE-443D-8B65-D6C987F4A80E}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {0B8ABEAD-D2B5-4370-A187-62B5ABE4EE50}

Microsoft.Maui-windows.slnf

@@ -27,6 +27,7 @@
       "src\\Controls\\tests\\Core.UnitTests\\Controls.Core.UnitTests.csproj",
       "src\\Controls\\tests\\CustomAttributes\\Controls.CustomAttributes.csproj",
       "src\\Controls\\tests\\DeviceTests\\Controls.DeviceTests.csproj",
+      "src\\Controls\\tests\\SourceGen.UnitTests\\SourceGen.UnitTests.csproj",
       "src\\Controls\\tests\\UITests\\Controls.AppiumTests.csproj",
       "src\\Controls\\tests\\Xaml.UnitTests.ExternalAssembly\\Controls.Xaml.UnitTests.ExternalAssembly.csproj",
       "src\\Controls\\tests\\Xaml.UnitTests.InternalsHiddenAssembly\\Controls.Xaml.UnitTests.InternalsHiddenAssembly.csproj",
@@ -47,7 +48,6 @@
       "src\\Graphics\\samples\\GraphicsTester.Android\\GraphicsTester.Android.csproj",
       "src\\Graphics\\samples\\GraphicsTester.Portable\\GraphicsTester.Portable.csproj",
       "src\\Graphics\\samples\\GraphicsTester.Skia.Console\\GraphicsTester.Skia.Console.csproj",
-      "src\\Graphics\\samples\\GraphicsTester.Skia.Tizen\\GraphicsTester.Skia.Tizen.csproj",
       "src\\Graphics\\samples\\GraphicsTester.Skia.Windows\\GraphicsTester.Skia.Windows.csproj",
       "src\\Graphics\\samples\\GraphicsTester.WinUI.Desktop\\GraphicsTester.WinUI.Desktop.csproj",
       "src\\Graphics\\samples\\GraphicsTester.iOS\\GraphicsTester.iOS.csproj",
@@ -63,14 +63,14 @@
       "src\\SingleProject\\Resizetizer\\test\\UnitTests\\Resizetizer.UnitTests.csproj",
       "src\\Templates\\src\\Microsoft.Maui.Templates.csproj",
       "src\\TestUtils\\samples\\DeviceTests.Sample\\TestUtils.DeviceTests.Sample.csproj",
-      "src\\TestUtils\\src\\UITest.Core\\UITest.Core.csproj",
-      "src\\TestUtils\\src\\UITest.Appium\\UITest.Appium.csproj",
-      "src\\TestUtils\\src\\UITest.NUnit\\UITest.NUnit.csproj",
       "src\\TestUtils\\src\\DeviceTests.Runners.SourceGen\\TestUtils.DeviceTests.Runners.SourceGen.csproj",
       "src\\TestUtils\\src\\DeviceTests.Runners\\TestUtils.DeviceTests.Runners.csproj",
       "src\\TestUtils\\src\\DeviceTests\\TestUtils.DeviceTests.csproj",
       "src\\TestUtils\\src\\Microsoft.Maui.IntegrationTests\\Microsoft.Maui.IntegrationTests.csproj",
       "src\\TestUtils\\src\\TestUtils\\TestUtils.csproj",
+      "src\\TestUtils\\src\\UITest.Appium\\UITest.Appium.csproj",
+      "src\\TestUtils\\src\\UITest.Core\\UITest.Core.csproj",
+      "src\\TestUtils\\src\\UITest.NUnit\\UITest.NUnit.csproj",
       "src\\Workload\\Microsoft.Maui.Sdk\\Microsoft.Maui.Sdk.csproj",
       "src\\Workload\\Microsoft.NET.Sdk.Maui.Manifest\\Microsoft.NET.Sdk.Maui.Manifest.csproj"
     ]