[release/7.0] Remove locks from COM events delegate management.

[github-actions]

Backport of #75863 to release/7.0

/cc @AaronRobinsonMSFT, @stephentoub

Customer Impact

This is a customer reported issue - #75863, both internal and external to Microsoft. The issue is triggering a COM Event A when handling a COM Event A. It represents a regression form .NET Framework. It was introduced in .NET Core 3.1, but as more people start to move onto .NET 5+ this will hit more. It is limited to COM Events so narrow in customer base, but those that use it will find it difficult to adopt as there is no workaround.

Testing

Validated this using a customer reproduction example. No new test was added due to the complexity of scenario and the narrowness of impact. The implementation was reduced in complexity substantially and is now more in line with best-practice concurrency related solutions in .NET Core.

Risk

This is a minor risk. Invoke locks were removed and immutability of a collection introduced. The reduction of complexity represented in the functional change makes this lower risk but the scenario is limited to COM Events which are even rarer so supporting a minor risk designation.

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Issue Details

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Backport of #75863 to release/7.0

/cc @AaronRobinsonMSFT

Customer Impact

Testing

Risk

IMPORTANT: Is this backport for a servicing release? If so and this change touches code that ships in a NuGet package, please make certain that you have added any necessary package authoring and gotten it explicitly reviewed.

Author:	github-actions[bot]
Assignees:	-
Labels:	area-System.Runtime.InteropServices
Milestone:	-

[jeffschwMSFT]

approved. please get a code review. we will take for consideration in 7 ga

[carlossanlop]

@AaronRobinsonMSFT don't forget to send the email to Tactics requesting approval, if you haven't done so.

[jeffschwMSFT]

We can take during tactics tomorrow

[JulieLeeMSFT]

@carlossanlop, this is approved over an email.

[carlossanlop]

Approved by Tactics, signed off, CI is green. Ready to merge.