Avoid stack overflows in CompositeEndpointDataSource

[halter73]

Avoid stack overflows in CompositeEndpointDataSource

This stack overflow is a little different than the stack overflow originally reported by a customer in #44085 when integrating YARP. However, it is a regression that could potentially be hit by non-YARP EndpointDataSource implementations.

I accidently hit this stack overflow when preparing an Ignite demo. And while there is a workaround to implement the custom EndpointDataSource more correctly by ensuring the custom GetChangeToken() implementation doesn't return the old change token while cancelling it, this did not cause a stack overflow or really any other problem in .NET 6, so this is a regression.

Fixes #44085

Customer Impact

EndpointDataSource is an advanced API, and defining a custom implementation that fires change tokens is rarer still. See https://grep.app/search?current=3&q=%3A%20EndpointDataSource for example usages.

Examining grep.app shows a few custom implementations that do fire a token, but the ones I've seen so far do so correctly in a way that will not trigger a stack overflow. All of the following examples replace the token before cancelling which works around this issue. I have not found any counterexamples yet.

• https://github.com/liuhll/silky/blob/3024012e23dfb4f84fba1c298dec35b7ec9ca9f1/framework/src/Silky.Http.Core/Routing/Builder/Internal/SilkyServiceEntryEndpointDataSource.cs#L92-L103
• https://github.com/microsoft/reverse-proxy/blob/c82a4a950417e7966447daeb2a333d19a87d722a/src/ReverseProxy/Management/ProxyConfigManager.cs#L705-L716
• https://github.com/aspnet/AspLabs/blob/ad32500f95d086f6e05e0a12050edb8da957ae4d/src/GrpcHttpApi/test/testassets/IntegrationTestsWebsite/Infrastructure/DynamicEndpointDataSource.cs#L55-L60

Regression?

• Yes
• No

And this is where I double checked and realized this isn't a regression lol. 😆 I still think this is a good change, but it's not worth servicing. I'll retarget to main.

Risk

• High
• Medium
• Low

[Justify the selection above]

Verification

• Manual (required)
• Automated

Packaging changes reviewed?

• Yes
• No
• N/A

[ghost]

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