[Categorical search] Connect FTRL ranking

This pulls together the FTRL optimizer with the other ranking logic
already implemented into two ranker instances, one for results and one
for categories. It also deletes several files that are now obsolete.
This makes the ranking structure:

1. Score normalization
2. FTRL result ranking using:
   - MRFU-based usage
   - score normalization
3. FTRL category ranking using:
   - MRFU-based usage
   - top-result-per-category
4. Best match ranking

Follow-up CLs will add other planned experts to the FTRL result ranking.
This CL has unit tests for ftrl_ranker, but some broader unit tests for
ranking as whole will be added in a follow-up.

Bug: 1199206
Change-Id: I482ca67647809cf0bb8bffc746774faf0bd20e62
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3394399
Reviewed-by: Rachel Wong <wrong@chromium.org>
Commit-Queue: Tony Yeoman <tby@chromium.org>
Cr-Commit-Position: refs/heads/main@{#960797}
20 files changed
tree: cd8866c66706b1df768b9841a141d1794326dff9
  1. android_webview/
  2. apps/
  3. ash/
  4. base/
  5. build/
  6. build_overrides/
  7. buildtools/
  8. cc/
  9. chrome/
  10. chromecast/
  11. chromeos/
  12. cloud_print/
  13. codelabs/
  14. components/
  15. content/
  16. courgette/
  17. crypto/
  18. dbus/
  19. device/
  20. docs/
  21. extensions/
  22. fuchsia/
  23. gin/
  24. google_apis/
  25. google_update/
  26. gpu/
  27. headless/
  28. infra/
  29. ios/
  30. ipc/
  31. jingle/
  32. media/
  33. mojo/
  34. native_client_sdk/
  35. net/
  36. pdf/
  37. ppapi/
  38. printing/
  39. remoting/
  40. rlz/
  41. sandbox/
  42. services/
  43. skia/
  44. sql/
  45. storage/
  46. styleguide/
  47. testing/
  48. third_party/
  49. tools/
  50. ui/
  51. url/
  52. weblayer/
  53. .clang-format
  54. .clang-tidy
  55. .eslintrc.js
  56. .git-blame-ignore-revs
  57. .gitattributes
  58. .gitignore
  59. .gn
  60. .mailmap
  61. .rustfmt.toml
  62. .vpython
  63. .vpython3
  64. .yapfignore
  65. AUTHORS
  66. BUILD.gn
  67. CODE_OF_CONDUCT.md
  68. codereview.settings
  69. DEPS
  70. DIR_METADATA
  71. ENG_REVIEW_OWNERS
  72. LICENSE
  73. LICENSE.chromium_os
  74. OWNERS
  75. PRESUBMIT.py
  76. PRESUBMIT_test.py
  77. PRESUBMIT_test_mocks.py
  78. README.md
  79. WATCHLISTS
README.md

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