Add Ribbon schema test to bloom_test (#7696)

Summary:
These new unit tests should ensure that we don't accidentally
change the interpretation of bits for what I call Standard128Ribbon
filter internally, available publicly as NewExperimentalRibbonFilterPolicy.
There is very little intuitive reason for the values we check against in
these tests; I just plug in the right expected values upon watching the
test fail initially.

Most (but not all) of the tests are essentially "whitebox" "round-trip." We
create a filter from fixed keys, and first compare the checksum of those
filter bytes against a saved value. We also run queries against other fixed
keys, comparing which return false positives against a saved set.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7696

Test Plan: test addition and refactoring only

Reviewed By: jay-zhuang

Differential Revision: D25082289

Pulled By: pdillinger

fbshipit-source-id: b5ca646fdcb5a1c2ad2085eda4a1fd44c4287f67