Make @PreviewApi a documented annotation.

[rlazo]

We want methods annotated with @PreviewApi to include it in their javadoc.

[github-actions]

Unit Test Results

1 205 tests  +413   1 189 ✔️ +397   1m 11s ⏱️ - 3m 37s
     89 suites +  29        16 💤 +  16 
     89 files   +  29          0 ❌ ±    0 

Results for commit 8222a12. ± Comparison against base commit af2a520.

[google-oss-bot]

Size Report ¹

Affected Products

• firebase-annotations

  Type	Base (af2a520)	Merge (f458ed2)	Diff
  apk (release)	8.88 kB	8.89 kB	+12 B (+0.1%)

Test Logs

• Base (af2a520): https://android-ci.firebaseopensource.com/view/gcs/android-ci/logs/postsubmit-binary-size/1556684385174949889
• Merge (f458ed2): https://android-ci.firebaseopensource.com/view/gcs/android-ci/pr-logs/pull/firebase_firebase-android-sdk/3976/binary-size/1557022875104317441

Notes

• Commit (f458ed2) is created by Prow via merging PR base commit (af2a520) and head commit (8222a12).

1. https://storage.googleapis.com/firebase-sdk-metric-reports/CgpyY4nqyE.html

[google-oss-bot]

Coverage Report ¹

Affected Products

No changes between base commit (af2a520) and merge commit (f458ed2).

Test Logs

• Base (af2a520): https://android-ci.firebaseopensource.com/view/gcs/android-ci/logs/postsubmit-check-coverage/1556684385174949893
• Merge (f458ed2): https://android-ci.firebaseopensource.com/view/gcs/android-ci/pr-logs/pull/firebase_firebase-android-sdk/3976/check-coverage-changed/1557022875100123138

Notes

• Commit (f458ed2) is created by Prow via merging PR base commit (af2a520) and head commit (8222a12).
• Run gradle <product>:checkCoverage to produce HTML coverage reports locally. After gradle commands finished, report files can be found under <product-build-dir>/reports/jacoco/.

1. https://storage.googleapis.com/firebase-sdk-metric-reports/UYLKeYGBZy.html