MuxLogger discrepancy introduced by new event

MuxLogger and normal logger have output difference of a blank line with the introduction of new event. The [Mux Logger test](https://github.com/maridematte/msbuild/blob/9fa9d800dabce3bfcf8365f651f3a713e01f8a85/src/Utilities.UnitTests/MuxLogger_Tests.cs#L129) was made more lenient so we could get work done without this being a blocker. This issue is being created to keep track of this difference and address it in the future.

## Context
When adding the new event `BuildSubmissionStartedEventArgs` (https://github.com/dotnet/msbuild/pull/10424) an unintentional side effect was changing how the logging output looks like. This is happening because there is a difference in event order between loggers.

Using the case of the `MockLogger`. The `MockLogger` will receive a `BuildStartedEvent`, log it, and then receive `BuildSubmissionStartedEvent`, log it, and then receive `ProjectStartedEvent` and log it.
```mermaid
flowchart LR
BS[BuildStartedEvent] --> BSS[BuildSubmissionStartedEvent] --> BS2[ProjectStartedEvent]
```

The MuxLogger will receive a `BuildStartedEvent`, ignore it, receive a `BuildSubmissionStartedEvent`, log it, and then receive `ProjectStartedEvent` when it will create an artificial `BuildStartedEvent` that will then log before logging `ProjectStartedEvent`.
```mermaid
flowchart LR
BS[BuildSubmissionStartedEvent] --> BSS[BuildStartedEvent] --> BS2[ProjectStartedEvent]
```

This causes the general event order to be different and for the outputs to be different.