[Group 4] Enable nullable annotations for Microsoft.Extensions.Logging.EventLog

[maxkoshevoi]

Related to #43605

Okay, so here's the thing. System.Diagnostics.EventLog is not annotated yet, and a lot of effort is needed to do it.
Here it's used only in WindowsEventLog which is internal, and nothing calls it with null, so it's should be safe to leave everything in is as non-nullable.

I may get around to annotate System.Diagnostics.EventLog in the future.

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Issue Details

---

Related to #43605

Okay, so here's the thing. System.Diagnostics.EventLog is not annotated yet, and a lot of effort is needed to do it.
Here it's used only in WindowsEventLog which is internal, and nothing calls it with null, so it's should be safe to leave everything in is as non-nullable.

I may get around to annotate System.Diagnostics.EventLog in the future.

Author:	maxkoshevoi
Assignees:	-
Labels:	new-api-needs-documentation, area-Extensions-Logging, community-contribution
Milestone:	-

[tarekgh]

@maryamariyan the changes here look good to me. Are you interested to take a quick look?