Fixes #12607 - Standardize usage of $PSItem and $_

[sdwheeler]

PR Summary

Standardize usage of $PSItem and $_

• Fixes AB#544994
• Fixes about_PSItem improvements/corrections #12607

PR Checklist

• Descriptive Title: This PR's title is a synopsis of the changes it proposes.
• Summary: This PR's summary describes the scope and intent of the change.
• Contributor's Guide: I have read the contributor's guide.
• Style: This PR adheres to the style guide.

[learn-build-service-prod]

PoliCheck Scan Report

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[learn-build-service-prod]

Learn Build status updates of commit fc6bae5:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/5.1/Microsoft.PowerShell.Core/About/about_Calculated_Properties.md	✅Succeeded	View (powershell-5.1)
reference/5.1/Microsoft.PowerShell.Core/About/about_PSItem.md	✅Succeeded	View (powershell-5.1)
reference/5.1/Microsoft.PowerShell.Core/About/about_Trap.md	✅Succeeded	View (powershell-5.1)
reference/5.1/Microsoft.PowerShell.Core/About/about_Try_Catch_Finally.md	✅Succeeded	View (powershell-5.1)
reference/7.4/Microsoft.PowerShell.Core/About/about_Calculated_Properties.md	✅Succeeded	View (powershell-7.4)
reference/7.4/Microsoft.PowerShell.Core/About/about_PSItem.md	✅Succeeded	View (powershell-7.4)
reference/7.4/Microsoft.PowerShell.Core/About/about_Trap.md	✅Succeeded	View (powershell-7.4)
reference/7.4/Microsoft.PowerShell.Core/About/about_Try_Catch_Finally.md	✅Succeeded	View (powershell-7.4)
reference/7.5/Microsoft.PowerShell.Core/About/about_Calculated_Properties.md	✅Succeeded	View (powershell-7.5)
reference/7.5/Microsoft.PowerShell.Core/About/about_PSItem.md	✅Succeeded	View (powershell-7.5)
reference/7.5/Microsoft.PowerShell.Core/About/about_Trap.md	✅Succeeded	View (powershell-7.5)
reference/7.5/Microsoft.PowerShell.Core/About/about_Try_Catch_Finally.md	✅Succeeded	View (powershell-7.5)
reference/7.6/Microsoft.PowerShell.Core/About/about_Calculated_Properties.md	✅Succeeded	View (powershell-7.6)
reference/7.6/Microsoft.PowerShell.Core/About/about_PSItem.md	✅Succeeded	View (powershell-7.6)
reference/7.6/Microsoft.PowerShell.Core/About/about_Trap.md	✅Succeeded	View (powershell-7.6)
reference/7.6/Microsoft.PowerShell.Core/About/about_Try_Catch_Finally.md	✅Succeeded	View (powershell-7.6)

For more details, please refer to the build report.