Changes made to pristine libwebp source by mozilla.org developers.

2023/03/06  -- Cherry-pick upstream fix (bug 1819244).

2022/02/03  -- Enabled automatic updates via Updatebot (meta bug #1618282). For
               further updates to the library please review the mercurial
               history for /media/libwebp/moz.yaml (bug #1753050).

2022/01/25  -- Synced with libwebp-1.2.2 (bug 1752025).

2021/09/08  -- Synced with libwebp-1.2.1 (bug 1729748).

2021/02/07  -- Synced with libwebp-1.2.0 (bug 1691317).

2020/02/26  -- Synced with libwebp-1.1.0 (bug 1618288).

2018/01/21  -- Synced with libwebp-1.0.2 (bug 1521478).

2018/11/26  -- Synced with libwebp-1.0.1 (bug 1509878).

2018/10/04  -- Synced with libwebp-1.0.0 (bug #1294490).