Fix PowerShell PostBuild failing when solution path contains spaces

[Myself-Bloons]

Summary

• Quote $(ProjectDir) and $(TargetDir) MSBuild properties in the PowerShell Copy-Item commands in ICSharpCode.Decompiler.PowerShell.csproj
• Without quotes, the PostBuild target fails with MSB3073 when the solution is cloned into a directory whose path contains spaces

Reproduction

1. Clone the repo into a folder with a space in its name (e.g. C:\Dev\ILSpy 10.0)
2. Run dotnet build ILSpy.sln --configuration Release
3. Build fails with: error MSB3073: The command "powershell -Command "Copy-Item ..." exited with code 1

Fix

Wrap the path arguments in single quotes so PowerShell treats them as literal string paths:

<Exec Command="powershell -Command &quot;Copy-Item '$(ProjectDir)manifest.psd1' '$(TargetDir)$(TargetName).psd1'&quot;" />

Test plan

• Verified build succeeds in a path with spaces (C:\Dev\IlySpy 10.0)
• 0 warnings, 0 errors on full solution build

[christophwille]

Thank you for your contribution!