Add language slugs (System.Diagnostics)

[gewarren]

Prep for dotnet/docs#45892.

(Hide whitespace changes.)

[dotnet-policy-service]

Tagging subscribers to this area: @tommcdon

[learn-build-service-prod]

Learn Build status updates of commit de08662:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Diagnostics.CodeAnalysis/FeatureSwitchDefinitionAttribute.xml	✅Succeeded	View
xml/System.Diagnostics.Tracing/EventSource.xml	✅Succeeded	View
xml/System.Diagnostics/Debug.xml	✅Succeeded	View
xml/System.Diagnostics/EventLog.xml	✅Succeeded	View
xml/System.Diagnostics/EventLogInstaller.xml	✅Succeeded	View
xml/System.Diagnostics/ProcessStartInfo.xml	✅Succeeded	View
xml/System.Diagnostics/XmlWriterTraceListener.xml	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

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

[BillWagner]

This LGTM @gewarren

Let's