Make linkcode_resolve() a bit more robust
This handles three cases that came up when adopting this snippet (for
finding source code corresponding to API docs) [for neuralgcm](https://github.com/google-research/neuralgcm/pull/58):
1. documenting class method or attributes
2. documenting properties
3. documenting `jit` decorated methods
I'm not sure if case (1) or (2) comes up in the JAX docs, but case (3)
definitely does -- `jit` decorated functions like `jax.nn.relu`
[currently do not](https://jax.readthedocs.io/en/latest/_autosummary/jax.nn.relu.html)
have source code link.
