Fix RS1038 Warning: Compiler extensions should be implemented in assemblies with compiler-provided references

[TheCodeTraveler]

Description of Change

This PR adds RS1038 to <WarningsAsErrors> and replaces Microsoft.CodeAnalysis.CSharp.Workspaces -> Microsoft.CodeAnalysis.CSharp

Link to RS1038 Docs:
https://github.com/dotnet/roslyn-analyzers/blob/main/docs/rules/RS1038.md

Additional information

Link to Compiler Warnings seen in CommunityToolkit.Maui: https://github.com/CommunityToolkit/Maui/actions/runs/15263232470/job/42928522628#step:14:61

Warning: D:\a\Maui\Maui\src\CommunityToolkit.Maui.Analyzers\UseCommunityToolkitInitializationAnalyzer.cs(9,2): warning RS1038: This compiler extension should not be implemented in an assembly containing a reference to Microsoft.CodeAnalysis.Workspaces. The Microsoft.CodeAnalysis.Workspaces assembly is not provided during command line compilation scenarios, so references to it could cause the compiler extension to behave unpredictably. (https://github.com/dotnet/roslyn-analyzers/blob/main/docs/rules/RS1038.md) [D:\a\Maui\Maui\src\CommunityToolkit.Maui.Analyzers\CommunityToolkit.Maui.Analyzers.csproj]

[Copilot]

Pull Request Overview

This PR fixes the RS1038 warning by replacing dependency references and ensuring that the RS1038 rule is treated as an error during compilation.

• Updated PackageReferences in multiple project files from Microsoft.CodeAnalysis.CSharp.Workspaces to Microsoft.CodeAnalysis.CSharp.
• Added RS1038 to the warnings-as-errors configuration in Directory.Build.props.

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/CommunityToolkit.Maui.SourceGenerators/CommunityToolkit.Maui.SourceGenerators.csproj	Updated dependency reference as per RS1038 recommendation.
src/CommunityToolkit.Maui.SourceGenerators.Internal/CommunityToolkit.Maui.SourceGenerators.Internal.csproj	Updated dependency reference as per RS1038 recommendation.
src/CommunityToolkit.Maui.MediaElement.Analyzers/CommunityToolkit.Maui.MediaElement.Analyzers.csproj	Updated dependency reference as per RS1038 recommendation.
src/CommunityToolkit.Maui.Camera.Analyzers/CommunityToolkit.Maui.Camera.Analyzers.csproj	Updated dependency reference as per RS1038 recommendation.
src/CommunityToolkit.Maui.Analyzers/CommunityToolkit.Maui.Analyzers.csproj	Updated dependency reference as per RS1038 recommendation.
Directory.Build.props	Added RS1038 rule to the warnings-as-errors and updated documentation for clarity.