Fix nested calls to Assembly Load Start tracing (#55700)

Fix nested calls to Assembly Load Start tracing (#55700)

The name_with_pid test ends up testing the behavior of event tracing in the presence of composite images.

In the presence of a composite image, it might happen attempting to send trace data may force an attempt to load System.Private.CoreLib thus causing an stackoverflow as attempting to report the load of System.Private.CoreLib will trigger a load of System.Private.CoreLib, etc. This fix steps around the issue by using a thread local variable to skip subsequent attempts to report the load of System.Private.CoreLib.

Fixes #55786