[FEA][torchinductor-EVT] Allow function source code to be passed directly to EVT tracer

[mlazos]

Is your feature request related to a problem? Please describe.
At

cutlass/python/cutlass/epilogue/epilogue.py

Line 117 in 5e49724

def trace(fn, example_tensors, **kwargs):

the trace(..) API takes in a function. The main issue here is that when dynamically defining a python function like so

fn = exec("""
def fn(x):
  return x
"""

extracting the source using inspect.getsource here fails.

This is how inductor generates the python source in essence (it generates a function string) so this does signature doesn't work.

Describe the solution you'd like
Modify the signature of trace to take the function source string directly.

cc @henrylhtsang, @eellison

[hwu36]

@jackkosaian

[jackkosaian]

@apuaaChen, can you help take a look at this EVT request?