Add target to fix analyzers on legacy .csproj projects

[Sergio0694]

Closes #540
Closes #495

This PR adds a new target to remove duplicate analyzers when running on legacy style .csproj projects.

Note: this does fix build errors, but IntelliSense is completely broken. Projects build but generated code isn't visible and is marked as errors. Analyzer warnings only show up in the output console but not in IntelliSense. Members referenced by generated code show up as unreferenced. The analyzers node in solution explorer is just completely empty and no analyzer is visible at all, so it's also impossible to inspect the generated code.

PR Checklist

• Created a feature/dev branch in your fork (vs. submitting directly from a commit on main)
• Based off latest main branch of toolkit
• PR doesn't include merge commits (always rebase on top of our main, if needed)
• Tested code with current supported SDKs
• Tests for the changes have been added (for bug fixes / features) (if applicable)
• Header has been added to all new source files (run build/UpdateHeaders.bat)
• Contains NO breaking changes
• Every new API (including internal ones) has full XML docs
• Code follows all style conventions