Fixes #11615 - Clarify facts about intrinsic properties Count and Length

[sdwheeler]

PR Summary

Clarify facts about intrinsic properties Count and Length

• Fixes AB#359487 - Fixes Incorrect assertion that intrinsic Count/Length properties are available to all collection types #11613
• Fixes AB#359488 - Fixes Recommend using Count to retrieve the number of elements in an in-memory collection #11614
• Fixes AB#359489 - Fixes Incorrect information on Count/Length properties of an array #11615

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.
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• Style: This PR adheres to the style guide.

[learn-build-service-prod]

Learn Build status updates of commit 3c07fe0:

✅ Validation status: passed

File	Status	Preview URL	Details
reference/5.1/Microsoft.PowerShell.Core/About/about_Arrays.md	✅Succeeded	View (powershell-5.1)
reference/5.1/Microsoft.PowerShell.Core/About/about_Intrinsic_Members.md	✅Succeeded	View (powershell-5.1)
reference/5.1/Microsoft.PowerShell.Core/About/about_Properties.md	✅Succeeded	View (powershell-5.1)
reference/7.4/Microsoft.PowerShell.Core/About/about_Arrays.md	✅Succeeded	View (powershell-7.4)
reference/7.4/Microsoft.PowerShell.Core/About/about_Intrinsic_Members.md	✅Succeeded	View (powershell-7.4)
reference/7.4/Microsoft.PowerShell.Core/About/about_Properties.md	✅Succeeded	View (powershell-7.4)
reference/7.5/Microsoft.PowerShell.Core/About/about_Arrays.md	✅Succeeded	View (powershell-7.5)
reference/7.5/Microsoft.PowerShell.Core/About/about_Intrinsic_Members.md	✅Succeeded	View (powershell-7.5)
reference/7.5/Microsoft.PowerShell.Core/About/about_Properties.md	✅Succeeded	View (powershell-7.5)

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