Update Roslyn 5.0 support in source generators

Refactored the Roslyn 5000 project to import shared props and projitems files. Added support for the ROSLYN_5_0_0_OR_GREATER constant, updated NoWarn conditions for RS2003, and introduced a temporary workaround for Roslyn 5.0.0 versioning in the props file.

Author: Sergio0694

src/CommunityToolkit.Mvvm.SourceGenerators.Roslyn5000/CommunityToolkit.Mvvm.SourceGenerators.Roslyn5000.csproj

@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
-  <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
-  </PropertyGroup>
+  <Import Project="..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.props" />
+  <Import Project="..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.projitems" Label="Shared" />
 
-</Project>
+</Project>

src/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.props

@@ -41,9 +41,13 @@
     <!-- Also define "ROSLYN_<MAJOR>_<MINOR>_OR_GREATER" build constants, so the generator code can multi-target whenever needed and add any required polyfills -->
     <DefineConstants Condition="$([MSBuild]::VersionGreaterThanOrEquals($(MvvmToolkitSourceGeneratorRoslynVersion), 4.3.1))">$(DefineConstants);ROSLYN_4_3_1_OR_GREATER</DefineConstants>
     <DefineConstants Condition="$([MSBuild]::VersionGreaterThanOrEquals($(MvvmToolkitSourceGeneratorRoslynVersion), 4.12.0))">$(DefineConstants);ROSLYN_4_12_0_OR_GREATER</DefineConstants>
+    <DefineConstants Condition="$([MSBuild]::VersionGreaterThanOrEquals($(MvvmToolkitSourceGeneratorRoslynVersion), 5.0.0))">$(DefineConstants);ROSLYN_5_0_0_OR_GREATER</DefineConstants>
 
     <!-- Disable the removed rules analyzer for older Roslyn versions (as we might not support all diagnostics) -->
-    <NoWarn Condition="$([MSBuild]::VersionLessThan($(MvvmToolkitSourceGeneratorRoslynVersion), 4.12.0))">$(NoWarn);RS2003</NoWarn>
+    <NoWarn Condition="$([MSBuild]::VersionLessThan($(MvvmToolkitSourceGeneratorRoslynVersion), 5.0.0))">$(NoWarn);RS2003</NoWarn>
+
+    <!-- Temporary workaround before GA -->
+    <MvvmToolkitSourceGeneratorRoslynVersion Condition="$([MSBuild]::VersionEquals($(MvvmToolkitSourceGeneratorRoslynVersion), 5.0.0))">5.0.0-2.final</MvvmToolkitSourceGeneratorRoslynVersion>
   </PropertyGroup>
 
   <ItemGroup>