Annotate Microsoft.Extensions.* assemblies for nullable reference types #43605

In .NET 6.0, we plan to annotate Microsoft.Extensions.* assemblies built from the dotnet/runtime repo. Work involves:

• Submit individual PRs, one for each assembly. Each PR should include changes to both the src and the ref. Each PR should contain only changes related to the nullable annotations/attributes, no other changes.
• PRs can be merged once the annotations have been appropriately reviewed in PR.

In .NET 5.0, nullable references types was tracked in #2339, and remainder are being tracked in #41720 for .NET 6.0

Group 1

• Microsoft.Extensions.DependencyInjection.Abstractions
• Microsoft.Extensions.Logging.Abstractions
• Microsoft.Extensions.Primitives ([Group 1] Enable nullable annotations for Microsoft.Extensions.Primitives #57395)
• Microsoft.Extensions.FileSystemGlobbing ([Group 1] Enable nullable annotations for Microsoft.Extensions.FileSystemGlobbing #57398)
• Microsoft.Extensions.DependencyModel

Group 2

• Microsoft.Extensions.Caching.Abstractions
• Microsoft.Extensions.Configuration.Abstractions
• Microsoft.Extensions.FileProviders.Abstractions
• Microsoft.Extensions.Options
• Microsoft.Extensions.DependencyInjection

Group 3

• Microsoft.Extensions.FileProviders.Physical
• Microsoft.Extensions.FileProviders.Composite
• Microsoft.Extensions.Hosting.Abstractions
• Microsoft.Extensions.Configuration
• Microsoft.Extensions.Logging
• Microsoft.Extensions.Caching.Memory
• Microsoft.Extensions.Options.DataAnnotation

Group 4

• Microsoft.Extensions.Configuration.Binder (Check first if System.ComponentModel.TypeConverter nullable enabled)
• Microsoft.Extensions.Configuration.CommandLine
• Microsoft.Extensions.Configuration.EnvironmentVariables
• Microsoft.Extensions.Configuration.FileExtensions
• Microsoft.Extensions.Http
• Microsoft.Extensions.Logging.EventLog (Check first if System.Diagnostics.EventLog nullable enabled)
• Microsoft.Extensions.Logging.EventSource
• Microsoft.Extensions.Logging.TraceSource (Check first if System.Diagnostics.TraceSource nullable enabled)
• Microsoft.Extensions.Logging.Debug

Group 5

• Microsoft.Extensions.Configuration.Ini
• Microsoft.Extensions.Configuration.Json
• Microsoft.Extensions.Configuration.Xml (Check first if System.Security.Cryptography.Xml nullable enabled)
• Microsoft.Extensions.Options.ConfigurationExtensions

Group 6

• Microsoft.Extensions.Configuration.UserSecrets
• Microsoft.Extensions.Logging.Configuration

Group 7

• Microsoft.Extensions.Logging.Console

Group 8

• Microsoft.Extensions.Hosting

Group 9

• Microsoft.Extensions.Hosting.Systemd
• Microsoft.Extensions.Hosting.WindowsServices

Guidance here: