Update NgenPriority to reduce number of priority 1 assemblies (#80411)

Changed two assemblies to be priority 2 to lower the duration of ngen for priority 1 assemblies. We are trying to improve how we ngen assemblies during installation to improve VS's startup, and as part of this are reducing the number of assemblies that have a priority of 1. JIT time during VS startup was used to determine the priorities, the following two assemblies are being changed to be priority 2:
- msbuild\current\bin\roslyn\microsoft.codeanalysis.csharp.dll
- msbuild\current\bin\roslyn\microsoft.codeanalysis.dll

Author: AlexDelepine

src/NuGet/Microsoft.Net.Compilers.Toolset/DesktopCompilerArtifacts.targets

@@ -28,8 +28,8 @@
     <ItemGroup>
 
       <!-- The Roslyn built binaries must be taken from these locations because this is the location where signing occurs -->
-      <DesktopCompilerArtifact Include="$(ArtifactsBinDir)Microsoft.CodeAnalysis\$(Configuration)\netstandard2.0\Microsoft.CodeAnalysis.dll" NgenArchitecture="all" NgenApplication="VBCSCompiler.exe" NgenPriority="1"/>
-      <DesktopCompilerArtifact Include="$(ArtifactsBinDir)Microsoft.CodeAnalysis.CSharp\$(Configuration)\netstandard2.0\Microsoft.CodeAnalysis.CSharp.dll" NgenArchitecture="all" NgenApplication="VBCSCompiler.exe" NgenPriority="1"/>
+      <DesktopCompilerArtifact Include="$(ArtifactsBinDir)Microsoft.CodeAnalysis\$(Configuration)\netstandard2.0\Microsoft.CodeAnalysis.dll" NgenArchitecture="all" NgenApplication="VBCSCompiler.exe" NgenPriority="2"/>
+      <DesktopCompilerArtifact Include="$(ArtifactsBinDir)Microsoft.CodeAnalysis.CSharp\$(Configuration)\netstandard2.0\Microsoft.CodeAnalysis.CSharp.dll" NgenArchitecture="all" NgenApplication="VBCSCompiler.exe" NgenPriority="2"/>
       <DesktopCompilerArtifact Include="$(ArtifactsBinDir)Microsoft.CodeAnalysis.Scripting\$(Configuration)\netstandard2.0\Microsoft.CodeAnalysis.Scripting.dll" NgenArchitecture="all" NgenApplication="csi.exe"/>
       <DesktopCompilerArtifact Include="$(ArtifactsBinDir)Microsoft.CodeAnalysis.CSharp.Scripting\$(Configuration)\netstandard2.0\Microsoft.CodeAnalysis.CSharp.Scripting.dll" NgenArchitecture="all" NgenApplication="csi.exe"/>
       <DesktopCompilerArtifact Include="$(ArtifactsBinDir)Microsoft.CodeAnalysis.VisualBasic\$(Configuration)\netstandard2.0\Microsoft.CodeAnalysis.VisualBasic.dll" NgenArchitecture="all" NgenApplication="VBCSCompiler.exe"/>