In #34897, the baseindex_tests unit test was introduced, meant for tests that test basic index functionality (e.g. reorg or unclean shutdown behavior) that should work regardless of the particular index type.
This PR moves two more of these tests (index_reorg_crash, coinstatsindex_unclean_shutdown) from test files of specific indexes into that folder.
In the second part, tests are executed sequentially for all index types instead of just one particular one, where applicable.
Before moving index_reorg_crash I extracted the BuildChain helper to util/mining so that it can be used by multiple tests. While doing that, I simplified the helper a bit.