Multi-platform build process (#1928)

* Add x86 to build process.

- Use recommended structure for multi-platform nuget.
- Separate build and pack to allow x64 and x86 builds.
- Use matrix in Github Actions to reduce repetition.

* Properly implement multi-platform nuget build.

- Split build pipeline to setting version, building and packing.
- Build AnyCPU only as reference assemblies.
- Add ref folder to nuget.

* Restructure project and pipeline.

Based on PR review discussion.

- Restore default x64,x86 build process.
  - Build generates platform specific nupkg.
  - Remove AnyCPU platform to prevent confusion.
- Add custom property for building reference libraries.
  - AnyCPU is only set by the property.
- Move nuget changes to separate target file.
  - Imported only when custom property is set.
  - Clear separation from the default build.
- Merge frameworks in published library artifacts.
- Re-simplify pipelines; no matrix or separate jobs.

LibreHardwareMonitorLib/LibreHardwareMonitorLib.csproj

@@ -19,12 +19,19 @@
     <PackageIcon>packageicon.png</PackageIcon>
     <GenerateResourceUsePreserializedResources>true</GenerateResourceUsePreserializedResources>
     <Platforms>x64;x86</Platforms>
+    <RuntimeIdentifiers>win-x64;win-x86</RuntimeIdentifiers>
+    <NoWarn>$(NoWarn);CA1416</NoWarn>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(BuildOnlyRefs)'=='true'">
+    <Platform>AnyCPU</Platform>
+    <ProduceOnlyReferenceAssembly>true</ProduceOnlyReferenceAssembly>
+    <GeneratePackageOnBuild>false</GeneratePackageOnBuild>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)'=='Debug'">
-    <OutputPath>..\bin\Debug\</OutputPath>
+    <OutputPath>..\bin\Debug\$(Platform)\</OutputPath>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)'=='Release'">
-    <OutputPath>..\bin\Release\</OutputPath>
+    <OutputPath>..\bin\Release\$(Platform)\</OutputPath>
   </PropertyGroup>
   <PropertyGroup>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
@@ -63,4 +70,5 @@
       <Pack>True</Pack>
     </None>
   </ItemGroup>
+  <Import Project="main.nuget.target" Condition="'$(PackMainNuget)' == 'true'" />
 </Project>