[templates] remove Directory.Build.targets, add @(ProjectCapability)

The `Directory.Build.targets` files in the templates were a collection
of workarounds that were needed until .NET MAUI was a workload. When
.NET MAUI was a NuGet package, this was the only way to set required
values for the IDE before NuGet restore. In the early days, you had to
unload/reload MAUI projects after NuGet restore.

We can remove `Directory.Build.targets` from templates now, and
consolidate `@(ProjectCapability)` so this is defined by the workload.

The following capabilities are defined for the IDE:

* `Maui`
* `MauiSingleProject`, `LaunchProfiles`, `XamarinStaticLaunchProfiles`
  when `$(SingleProject)` is `true`

These new capabilities are defined to identify projects (via telemetry)
that bring in portions of .NET MAUI:

* `MauiAssets`
* `MauiBlazor`
* `MauiCore`
* `MauiEssentials`

Other changes:

* `$(_KeepLaunchProfiles)` is set by default when `$(SingleProject)`
  is `true`.
* WinUI workarounds are moved into `WinUI.SingleProject.targets`.
* Fixed `sdk-manifests` casing for `src/DotNet/DotNet.csproj -t:Install`

.nuspec/Microsoft.Maui.Controls.SingleProject.targets

@@ -1,6 +1,8 @@
 <!-- "Single Project" support -->
 <Project>
   <PropertyGroup Condition=" '$(SingleProject)' == 'true' ">
+    <!-- Required - Enable Launch Profiles for .NET 6 iOS/Android -->
+    <_KeepLaunchProfiles>true</_KeepLaunchProfiles>
     <!-- Android -->
     <EnableDefaultAndroidItems>false</EnableDefaultAndroidItems>
     <AndroidProjectFolder Condition=" '$(AndroidProjectFolder)' == '' ">Android\</AndroidProjectFolder>
@@ -60,5 +62,11 @@
   <ItemGroup Condition=" '$(SingleProject)' == 'true' ">
     <ProjectCapability Include="MauiSingleProject" />
     <ProjectCapability Include="LaunchProfiles" />
+    <!--
+      Optional - Enables a list of TFM's and device categories in the debug menu.
+      This allows easily toggling of debug target TFM by selecting the platform.
+      If removed, top level debug targets show as a list of devices for the selected TFM.
+      -->
+    <ProjectCapability Include="XamarinStaticLaunchProfiles" />
   </ItemGroup>
 </Project>

src/DotNet/DotNet.csproj

@@ -57,7 +57,7 @@
       <_WorkloadFiles Include="$(_InstallTempDirectory)data/WorkloadManifest.*" />
     </ItemGroup>
     <CopyWorkloadFiles
-        Name="Microsoft.NET.Sdk.Maui"
+        Name="microsoft.net.sdk.maui"
         Files="@(_WorkloadFiles)"
         WorkloadDirectory="$(MSBuildExtensionsPath)../../sdk-manifests/$(DotNetPreviewVersionBand)"
         VersionBand="$(DotNetPreviewVersionBand)"

src/Workload/Microsoft.Maui.Controls.Sdk/Sdk/Microsoft.Maui.Controls.Sdk.After.targets

@@ -12,4 +12,11 @@
     <Analyzer Include="$(MSBuildThisFileDirectory)../targets/Microsoft.Maui.Controls.Xaml.dll" />
     <Analyzer Include="$(MSBuildThisFileDirectory)../targets/Microsoft.Maui.Controls.SourceGen.dll" />
   </ItemGroup>
+  <!-- @(ProjectCapability) used to identify parts of Maui -->
+  <ItemGroup>
+    <ProjectCapability Include="MauiAssets"     Condition=" '$(UseMaui)' == 'true' or '$(UseMauiAssets)' == 'true' " />
+    <ProjectCapability Include="MauiBlazor"     Condition=" '$(UsingMicrosoftNETSdkRazor)' == 'true' " />
+    <ProjectCapability Include="MauiCore"       Condition=" '$(UseMaui)' == 'true' or '$(UseMauiCore)' == 'true' " />
+    <ProjectCapability Include="MauiEssentials" Condition=" '$(UseMaui)' == 'true' or '$(UseMauiEssentials)' == 'true' " />
+  </ItemGroup>
 </Project>

src/Workload/Microsoft.Maui.Controls.Sdk/Sdk/WinUI.SingleProject.targets

@@ -0,0 +1,6 @@
+<!-- Workarounds for WinUI when $(SingleProject) is true -->
+<Project>
+  <!-- Required - Overwrite tasks that are not needed when multitargeting -->
+  <Target Name="ValidateWinUIPlatform" />
+  <Target Name="BinPlaceBootstrapDll" />
+</Project>

src/Workload/Microsoft.Maui.Controls.Sdk/Sdk/WinUI.targets

@@ -8,4 +8,5 @@
       />
     </ItemGroup>
   </Target>
+  <Import Project="WinUI.SingleProject.targets" Condition=" '$(SingleProject)' == 'true' " />
 </Project>