[dynamo] Trace through builtin `abs` (#110398)
In python `abs(x)` does nothing but delegate to `x.__abs__()` so we should do
the same in dynamo. This also adds `SymNode.__abs__` so we can trace through
indexing expressions involving `abs`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/110398
Approved by: https://github.com/jansel, https://github.com/lezcano
