[FX] OSS is_fx_tracing (#80255)
Summary:
Enable a flag in tracer to export the status of the tracing rather than checking the module call function.
Context: Feature_processor needs is_fx_tracing and currently this function is implemented by PyPer and cannot be OSS. We want to open source this function and implement it inside Fx Tracer
Test Plan: test in the stacked diff D37386855
Reviewed By: jamesr66a
Differential Revision: D37386820
Pull Request resolved: https://github.com/pytorch/pytorch/pull/80255
Approved by: https://github.com/jamesr66a
