.NET projects produce a reference assembly by default (#8571)

In general we want to produce reference assemblies whenever possible, as they improve incremental build performance.

Making them work end-to-end requires support from other components, such as fast up-to-date checks in VS. While support was originally added for SDK-style projects, it was not present for legacy `.csproj` files. Accordingly, `ProduceReferenceAssemblies` was set `true` only when the target framework was `net5.0` or later for C#/VB projects. Similarly, F# added support during `net7.0`, so a similar check was added for F# projects.

VS 17.5 ships support for reference assemblies in the legacy CSPROJ fast up-to-date check, so all C#/VB projects are supported. Similarly, F# has full support. Consequently, it is now safe to enable the production and consumption of reference assemblies across all .NET project types, including .NET Framework, .NET Standard, .NET Core and .NET.

This commit changes the default `ProduceReferenceAssembly` value to `true` for all .NET projects that don't set `ProduceOnlyReferenceAssembly`.

Author: drewnoakes

src/Tasks/Microsoft.NET.props

@@ -7,13 +7,22 @@ WARNING:  DO NOT MODIFY this file unless you are knowledgeable about MSBuild and
           impossible to load or build your projects from the command-line or the IDE.
 
 This file contains .NET-specific properties, and items. This file is imported for .NET Core, .NET Standard, and .NET Framework projects.
-these two files are used to encapsulate the multi-targeting and framework specific build process.
 
 Copyright (C) Microsoft Corporation. All rights reserved.
 ***********************************************************************************************
 -->
 <Project>
 
+  <!--
+    ============================================================
+                                        Reference Assemblies
+    Enable the production of a reference assembly by all .NET projects, by default.
+    ============================================================
+  -->
+  <PropertyGroup>
+    <ProduceReferenceAssembly Condition=" '$(ProduceReferenceAssembly)' == '' and '$(ProduceOnlyReferenceAssembly)' != 'true' ">true</ProduceReferenceAssembly>
+  </PropertyGroup>
+
   <!--
     ============================================================
                                         GetToolPaths