Add EventWaitHandle creation extension method that takes an ACL

[carlossanlop]

Approved API Proposal: https://github.com/dotnet/corefx/issues/41662

Description

We don't currently have a way to create an EventWaitHandle with a given ACL in .NET Core. We can modify the ACL, but it would be more secure to have the proper ACL on the object from the start.

Customer impact

Before this change, customers had to create an EventWaitHandle, then set its ACLs. This presents a few problems:

• Potential security hole as event wait handles can be accessed between creation and modification.
• Porting difficulties as there isn't a 1-1 API replacement

This change addresses those problems by adding a new extension method that allows creating an EventWaitHandle and ensuring the provided ACLs are set during creation.

This change is expected to be backported to 3.1.

[danmoseley]

BTW, unlike System.IO.FileSystem.AccessControl, System.Threading.AccessControl package is not in netcoreapp. Therefore if this was backported to servicing (which I was assuming would not happen anyway, since today's the last day), it would presumably need package authoring as well .cc @ericstj

[stephentoub]

Other than my test comments, LGTM.

[JeremyKuhne]

Nothing to add beyond Stephen's nits. Looks good.