Extract helper code for Analyzers and Source Generators

ExternalProjects/AnalyzersCommon.props

@@ -0,0 +1,16 @@
+<Project>
+	<!--
+		This is a set of MSBuild imports rather than a project because I COULD NOT for the life of me get the latter to work.
+		With the workaround given in dotnet/roslyn#61940, everything built, but then the main solution wouldn't build. Every project gave:
+			warning CS8785: Generator 'VIMGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result.
+			Exception was of type 'FileNotFoundException'
+			with message 'Could not load file or assembly 'BizHawk.Analyzers.Common, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. The system cannot find the file specified.
+		Yes, even with an EXPLICIT <Reference/> to the Common project's assembly. So you get this instead. —yoshi
+	-->
+	<Import Project="LibCommon.props" />
+	<ItemGroup>
+		<PackageReference Include="Microsoft.CodeAnalysis.Analyzers" Version="3.3.2" />
+		<PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.8.0" />
+		<Compile Include="$(ProjectDir)../AnalyzersCommon/**/*.cs" />
+	</ItemGroup>
+</Project>

ExternalProjects/AnalyzersCommon/RoslynUtils.cs

@@ -4,7 +4,7 @@ using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 
-internal static class RoslynUtils
+public static class RoslynUtils
 {
 	public static SyntaxNode? EnclosingTypeDeclarationSyntax(this CSharpSyntaxNode node)
 	{

ExternalProjects/BizHawk.Analyzer/BizHawk.Analyzer.csproj

@@ -2,12 +2,5 @@
 	<PropertyGroup>
 		<TargetFramework>netstandard2.0</TargetFramework>
 	</PropertyGroup>
-	<Import Project="../LibCommon.props" />
-	<PropertyGroup>
-		<NoWarn>$(NoWarn);SA1200</NoWarn>
-	</PropertyGroup>
-	<ItemGroup>
-		<PackageReference Include="Microsoft.CodeAnalysis.Analyzers" Version="3.3.2" PrivateAssets="all" />
-		<PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.8.0" PrivateAssets="all" />
-	</ItemGroup>
+	<Import Project="../AnalyzersCommon.props" />
 </Project>

ExternalProjects/BizHawk.SrcGen.ReflectionCache/BizHawk.SrcGen.ReflectionCache.csproj

@@ -2,9 +2,5 @@
 	<PropertyGroup>
 		<TargetFramework>netstandard2.0</TargetFramework>
 	</PropertyGroup>
-	<Import Project="../LibCommon.props" />
-	<ItemGroup>
-		<PackageReference Include="Microsoft.CodeAnalysis.Analyzers" Version="3.3.2" PrivateAssets="all" />
-		<PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.8.0" PrivateAssets="all" />
-	</ItemGroup>
+	<Import Project="../AnalyzersCommon.props" />
 </Project>

ExternalProjects/LibCommon.props

@@ -1,6 +1,7 @@
 <Project>
 	<Import Project="../Common.props" />
 	<PropertyGroup>
+		<NoWarn>$(NoWarn);SA1200</NoWarn>
 		<RunAnalyzersDuringBuild>true</RunAnalyzersDuringBuild>
 	</PropertyGroup>
 	<ItemGroup>