Port System.Collections (once again)

[carlossanlop]

Found some newly added docs. @dotnet/area-system-collections

Please review ignoring whitespace

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Issue Details

---

Found some newly added docs. @dotnet/area-system-collections

Please review ignoring whitespace

Author:	carlossanlop
Assignees:	carlossanlop
Labels:	area-System.Collections
Milestone:	-

[learn-build-service-prod]

Learn Build status updates of commit 46fa942:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Collections.Frozen/FrozenDictionary`2.xml	✅Succeeded	View
xml/System.Collections.Frozen/FrozenDictionary`2+Enumerator.xml	✅Succeeded	View
xml/System.Collections.Frozen/FrozenSet`1.xml	✅Succeeded	View
xml/System.Collections.Frozen/FrozenSet`1+Enumerator.xml	✅Succeeded	View
xml/System.Collections.Generic/CollectionExtensions.xml	✅Succeeded	View
xml/System.Collections.Generic/EqualityComparer`1.xml	✅Succeeded	View
xml/System.Collections.Generic/List`1.xml	✅Succeeded	View
xml/System.Collections.Generic/SortedSet`1.xml	✅Succeeded	View
xml/System.Collections.ObjectModel/ReadOnlyCollection`1.xml	✅Succeeded	View
xml/System.Collections.ObjectModel/ReadOnlyDictionary`2.xml	✅Succeeded	View
xml/System.Collections.ObjectModel/ReadOnlyDictionary`2+KeyCollection.xml	✅Succeeded	View
xml/System.Collections.ObjectModel/ReadOnlyObservableCollection`1.xml	✅Succeeded	View

For more details, please refer to the build report.

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