PR Summary

Replace if not null-checks with null propagation operator to solve IDE0031 with .NET Preview 7.

PR Context

Related to #17769

PR Checklist

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• Breaking changes
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• User-facing changes
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  • Documentation needed
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  • N/A or can only be tested interactively
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    • Impact on PowerShell Editor Services which is used in the PowerShell extension for VSCode
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