[release/10.0] [EventPipe][UserEvents] Allow empty tracepoint sets

[github-actions]

Backport of #119651 to release/10.0

/cc @mdh1418

Customer Impact

• Customer reported
• Found internally

This impacts user_events-based EventPipe Sessions, which is a .NET 10 Linux-only feature.

Before the change, valid IPC command payloads to start a user_events-based eventpipe session would be incorrectly deemed invalid and thus the session wouldn't start.

Specifically, the specification at https://github.com/dotnet/diagnostics/blob/main/documentation/design-docs/ipc-protocol.md#user_events-session-payload dictates that the tracepoint_sets payload portion can be empty if the default_tracepoint_name was present, but the previous logic considered that invalid.

The expectation is that just specifying the default tracepoint name and 0 tracepoint sets for a provider configuration would still kickoff a user_events-based eventpipe session.

Regression

• Yes
• No

Testing

Manually tested with custom script to send an IPC command.

Risk

Low. The change affects the IPC command parsing logic for user_events-based eventpipe sessions, a .NET 10 feature. Previously, some payloads were incorrectly deemed invalid, preventing user_events-based eventpipe sessions from being started. Now, the runtime will deem them valid and allow the eventpipe session to start.

[jeffschwMSFT]

approved. please get a code review. we can merge when ready

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[mdh1418]

Looks like Build Analysis did find the related issue, but didn't actually turn green? Is that because the table wasn't updated in the known issue?

[hoyosjs]

@mdh1418 - build analysis doesn't do that on release branches.

[hoyosjs]

/ba-g all issues are known - this is a release branch which doesn't turn green automatically.