WPF: CleanupTemporaryTargetAssembly step after MarkupCompilePass2 intermittently fails to delete target assembly

_This issue has been moved from [a ticket on Developer Community](https://developercommunity.visualstudio.com/t/WPF:-CleanupTemporaryTargetAssembly-step/1447628)._

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[severity:Multiple people on my team are impacted (internal MSFT only)]
Some WPF projects require a second pass compile, in which a temporary project is generated and then cleaned up. Sometimes, during this compilation, the "CleanupTemporaryTargetAssembly" step fails to perform cleanup successfully due to the target assembly being locked.

Sample error:
```
MarkupCompilePass2:
MarkupCompilePass2 successfully generated BAML or source code files.
CleanupTemporaryTargetAssembly:
Deleting file "Debug\AnyCPU\MyWpfAssembly.dll".
##[error]C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.WinFx.targets(480,10): Error MSB3061: Unable to delete file "Debug\AnyCPU\MyWpfAssembly.dll". The process cannot access the file 'C:\w\4\s\src\MyWpfAssembly\Debug\AnyCPU\MyWpfAssembly.dll' because it is being used by another process.
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.WinFx.targets(480,10): error MSB3061: Unable to delete file "Debug\AnyCPU\MyWpfAssembly.dll". The process cannot access the file 'C:\w\4\s\src\MyWpfAssembly\Debug\AnyCPU\MyWpfAssembly.dll' because it is being used by another process. [C:\w\4\s\src\MyWpfAssembly\MyWpfAssembly.csproj]
Done Building Project "C:\w\4\s\src\MyWpfAssembly\MyWpfAssembly.csproj" (default targets) -- FAILED.

```

Other customers have reported the same issue, ex.
https://social.msdn.microsoft.com/Forums/en-US/6360a1e3-a269-457c-a763-fb415b8bbf14/quotbecause-it-is-being-used-by-another-processquot-error-has-me-dead-in-the-water?forum=msbuild

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### Original Comments

#### Feedback Bot on 6/11/2021, 08:22 AM:

We have directed your feedback to the appropriate engineering team for further evaluation. The team will review the feedback and notify you about the next steps.

#### Chaitanya Mangalagiri [MSFT] on 8/12/2021, 00:50 AM:

(private comment, text removed)

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### Original Solutions
(no solutions)