Add APIs for allocation-free delegate invocation list inspection

[jkotas]

Fixes #41849

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Issue Details

---

Fixes #41849

Author:	jkotas
Assignees:	-
Labels:	area-System.Runtime, new-api-needs-documentation
Milestone:	-

[stephentoub]

Nice.

[stephentoub]

Looks like there are a few places we could use HasSingleTarget, e.g.

runtime/src/libraries/System.ObjectModel/src/System/Collections/ObjectModel/ObservableCollection.cs

Line 231 in 2d49c2f

if (CollectionChanged?.GetInvocationList().Length > 1)

runtime/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/BindingList.cs

Line 304 in 2d49c2f

private bool AddingNewHandled => _onAddingNew != null && _onAddingNew.GetInvocationList().Length > 0;

(though I don't understand that second one... won't _onAddingNew.GetInvocationList().Length > 0 always be true?)

[stephentoub]

And a few places we could enumerate more cheaply?

runtime/src/libraries/System.Private.CoreLib/src/System/Runtime/Loader/AssemblyLoadContext.cs

Line 630 in 2d49c2f

foreach (Func<AssemblyLoadContext, AssemblyName, Assembly> handler in resolvingHandler.GetInvocationList())

runtime/src/libraries/System.Private.CoreLib/src/System/Runtime/Loader/AssemblyLoadContext.cs

Line 744 in 2d49c2f

foreach (ResolveEventHandler handler in eventHandler.GetInvocationList())

runtime/src/libraries/System.Private.CoreLib/src/System/Runtime/Loader/AssemblyLoadContext.cs

Line 825 in 2d49c2f

foreach (Func<Assembly, string, IntPtr> handler in dllResolveHandler.GetInvocationList())

[jkotas]

All failures are known according to the build analysis