WiX: rework the SDK layout

Restore the components, move the install location, and enable the
dual-purpose installer, and enable higher compression.  The higher
compression helps offset some of the associated costs for the split
MSIs.

The SDKs are now relocated to `%ProgramFiles%\Swift\Platforms` to
co-locate the Platform SDKs with the toolchain and runtime.  The
conversion to a dual purpose MSI will relocate this to
`%LocalAppData%\Programs\Swift\Platforms`.  In most cases this should be
a space free path which allows us to finally migrate away from
`C:\Library` and fix the issue of incorrect permissions on directories.

Author: compnerd

platforms/Windows/sdk.wixproj

@@ -27,6 +27,21 @@
     <HarvestGenerateGuidsNow>true</HarvestGenerateGuidsNow>
   </PropertyGroup>
 
+  <PropertyGroup Condition=" '$(ProductArchitecture)' == 'amd64' ">
+    <InstallerPlatform>x64</InstallerPlatform>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(ProductArchitecture)' == 'arm64' ">
+    <InstallerPlatform>arm64</InstallerPlatform>
+    <InstallerVersion>500</InstallerVersion>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(ProductArchitecture)' == 'arm' ">
+    <InstallerPlatform>arm</InstallerPlatform>
+    <InstallerVersion>500</InstallerVersion>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(ProductArchitecture)' == 'x86' ">
+    <InstallerPlatform>x86</InstallerPlatform>
+  </PropertyGroup>
+
   <ItemGroup>
     <PackageReference Include="WixToolset.UI.wixext" Version="4.0.0" />
     <PackageReference Include="WixToolset.Heat" Version="4.0.0" />