Add obj/bin folder deletion solution to CS0518 compiler error documentation (#47627)

* Initial plan

* Add obj/bin deletion solution to CS0518 documentation

Co-authored-by: BillWagner <[email protected]>

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Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: BillWagner <[email protected]>
Co-authored-by: Bill Wagner <[email protected]>

Author: Copilot

docs/csharp/language-reference/compiler-messages/cs0518.md

@@ -52,3 +52,5 @@ The main cause for this problem is that the project cannot access the predefined
 - Reinstall the .NET Framework common language runtime (if the previous solutions do not solve the problem).
 
 - Reload the project in Visual Studio.
+
+- Close Visual Studio, delete the `obj` and `bin` folders from your project directory, then reopen Visual Studio and rebuild the project.