Refactor symbolfile script

Introduce the class `Filter` which encapsulates conditions
(architecture, api level, whether llndk is included, etc.) so that we
don't need to touch many places everytime a new condition is added.

In addition, refactor test_symbolfile to reduce duplications

This CL doesn't add a new functionality.

Bug: 239274367
Test: run test_ndkstubgen and test_symbolfile
Change-Id: I188e482492d39ec18134ecc5c908f0d288a754a9