Fix NullReferenceException in background thread emitting IL in Depend…

[eerhardt]

…encyInjection

When ILEmitResolverBuilder is getting created, it grabs the "Root" scope off of the ServiceProvider. However, the Root scope isn't set on ServiceProvider yet. So later when it tries to get used, it null refs. But this exception gets caught an eaten since it happens on a background thread.

The fix is to set Root before creating the ServiceProviderEngine.

See description of the issue in #55255 (comment).

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Issue Details

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…encyInjection

When ILEmitResolverBuilder is getting created, it grabs the "Root" scope off of the ServiceProvider. However, the Root scope isn't set on ServiceProvider yet. So later when it tries to get used, it null refs. But this exception gets caught an eaten since it happens on a background thread.

The fix is to set Root before creating the ServiceProviderEngine.

Author:	eerhardt
Assignees:	-
Labels:	area-Extensions-DependencyInjection
Milestone:	-

[davidfowl]

I'm betting this it the cause of the performance regression on ARM.

[davidfowl]

One small nit

[pakrym]

What do you think about adding a Debug.Assert to https://github.com/dotnet/runtime/blob/main/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceLookup/DynamicServiceProviderEngine.cs#L39 ?

[eerhardt]

Installer Build and Test coreclr Linux_arm64 Release test failure is infrastructure related, and unrelated to this change.