[compiled autograd] refactor eager test loading and run custom ops tests (#120679)
TestCustomOp's tests uses helper attributes and functions from a util parent class. To support arbitrary test classes, we need to refactor the current approach. Instead of allowlisting certain methods, we can instead copy the whole class and only overwrite the "test_.*" methods.
Compiled autograd fails on ~10/90 of the newly added tests. test_autograd_function_backed_op is the example we discussed in PT-2D meeting about requiring c++ autograd::Function support. I'm addressing this in #120732
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120679
Approved by: https://github.com/jansel, https://github.com/zou3519
