Update SafeHandle doc around CER

[AaronRobinsonMSFT]

Summary

Clarify details on DangerousAddRef and remove mentions of CER.

Related microsoft/CsWin32#753

[AaronRobinsonMSFT]

/cc @stephentoub

[opbld34]

Learn Build status updates of commit a6f7880:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Runtime.InteropServices/SafeHandle.xml	✅Succeeded	View

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Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

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[opbld30]

Learn Build status updates of commit 9d9725c:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Runtime.InteropServices/SafeHandle.xml	✅Succeeded	View

For more details, please refer to the build report.

Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

For any questions, please:

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• Post your question in the Learn support channel

[opbld33]

Learn Build status updates of commit 308c01b:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Runtime.InteropServices/SafeHandle.xml	✅Succeeded	View

For more details, please refer to the build report.

Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel