[changelog] Add 19.0.x, 19.1.x, 19.2.x patch releases (#36898)

Documents the patch releases that shipped across the 19.0, 19.1, and
19.2 lines (`.2`/`.3` through `.7`/`.8`), which were missing from the
changelog.

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Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>