[Default interfaces] Debugger support

[MichalStrehovsky]

This tracks checking whether we need any work on the debugger side to be able to invoke default interface methods and if any work is needed, this will track the work in question.

At minimum, we'll need:

• Support for invoking shared instance methods on generic interfaces. Those are kind of special.
• Stepping into/over interface calls that hit the diamond inheritance problem. (These throw exception in an unexpected place.)

[lt72]

@noahfalk @mikem8361 FYI

[noahfalk]

To the list above I suggest adding:

• ENC tracked here: https://github.com/dotnet/coreclr/issues/16023
• VS debugger support in the IL interpreter (adding @plnelson)
• Manual testing of the VS debugger when using default interfaces
• Update our automated debugger tests with at least one successful default interface case and one diamond pattern ambiguous default interface case. The test should cover stepping, func-eval, breakpoint inside the default implementation, and viewing the callstack. We should be able to get someone on @tommcdon's team to help when you are ready.

Looking into the stepping issue I think you were accurate in predicting trouble at that spot. I filed dotnet/coreclr#22059 with my best guess on what in the code needs to be fixed.

[sergiy-k]

@tommcdon, could you please route this issue? Should be assigned to someone on your team?

[noahfalk]

Historically teams that build new runtime features own the testing of those features across all the perpendiculars. I think its reasonable for the diagnostics team to assist with adding a new regression test, running it for you in the future + the general consulting/assistance we already did, but not to own this work item all up.

[tommcdon]

Closing as the work to support default interfaces is done to the best of our knowledge