Fix index rewriter to rewrite all Or/AndPredicates

ChangeIndexRewriter processes predicate tree to group all index
predicates into one at each level. Rewriter starts from root node
and traverses to all the child nodes. Rewriter recursively marks each
child predicate as indexed or nonindexed. Then it partitions all the
indexed predicates together and also rewrites And/OrPredicates to
either a source or a cardinal predicate. Before this change, rewriter
short-circuits the partitioning & skips rewrite logic when there is
only one indexed child. Due to this behavior, query [2] was not
rewritten to OrCardinal predicate since (status:open OR status:merged)
is one indexed child at its level (as in [3]), whereas query [1] was
rewritten to AndCardinal.

[1] status:open age:1d issue:123
[2] (status:open OR status:merged) issue:123
[3]    root
       / \
     Or  issue:123
    / \
 open merged

Fix index rewriter to run the rewrite logic to rewrite Or/AndPredicate
to respective cardinal predicates when it short-circuits. This helps
AndSource to choose the right source more often. Also fix few tests
to assert on OrCardinalPredicate rather than OrPredicate.

Unfortunately there are no operators which are datasources other
than Index in the Core as of now. We at Qualcomm have a datasource
operator in a plugin which takes a bug number and queries the bug
tracker's DB for changes related to that bug number. Suppose this
operator (say issue:123) returns around 15 changes. On a 3.4 test site
against LUCENE which contains ~20K open changes, ~2.8M merged changes,
the performance of,

query "(status:open OR status:merged) issue:123"
  before: 6m52s, 6m40s, 6m36s
  after: 0.07s, 0.07s, 0.07s

Release-Notes: AndSource chooses right source more often
Change-Id: I87311359e28795d5f461b233cecd82ecaf53ee57
2 files changed
tree: 408d59d6ded6aed07a0ee0c397a862f0272ca865
  1. .settings/
  2. .ts-out/
  3. antlr3/
  4. contrib/
  5. Documentation/
  6. e2e-tests/
  7. java/
  8. javatests/
  9. lib/
  10. modules/
  11. plugins/
  12. polygerrit-ui/
  13. prolog/
  14. prologtests/
  15. proto/
  16. resources/
  17. tools/
  18. webapp/
  19. .bazelignore
  20. .bazelproject
  21. .bazelrc
  22. .bazelversion
  23. .editorconfig
  24. .git-blame-ignore-revs
  25. .gitignore
  26. .gitmodules
  27. .gitreview
  28. .mailmap
  29. .pydevproject
  30. .zuul.yaml
  31. BUILD
  32. COPYING
  33. INSTALL
  34. Jenkinsfile
  35. package.json
  36. README.md
  37. SUBMITTING_PATCHES
  38. version.bzl
  39. WORKSPACE
  40. yarn.lock
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