• real fix needs to happen in TraceEvent

As noted in #44072, the intermittent failure is caused by the reader (EventPipeEventSource) indefinitely pausing while trying to read bytes to reach 8-byte alignment. EventBlocks are not required to be aligned lengths. There are only 2 events associated with the keyword EEStartupStart belongs to, so once those events have been received there won't be more data sent. If the EventBlock containing those events is not an 8-byte aligned size, the reader will read the EventBlock, but not dispatch the events until it receives enough data to fill the alignment requirement. That data won't arrive, so the test fails with the reader never reporting that the EEStartupStart event fired.

The bandaid fix is to put another provider on the test that guarantees there will be more data to read and the EventBlock containing EEStartupStart will get dispatched by EventPipeEventSource. In this case, I'm adding Microsoft-DotNETCore-SampleProfiler, but theoretically any other provider that generates an event would be sufficient.

I'm hacking up a patch for the reader code in TraceEvent that will prevent this corner case, but that will take time to flow into the runtime repo, so this bandaid will do for now.

I'll open the PR in draft mode to run the CI a few times through and then mark it for review. I want these tests turned back on before we complete #46079.

CC @tommcdon @noahfalk @sywhang @lateralusX @brianrob