Fix typo s/range of change/rate of change/

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extra : rebase_source : 5b66545336fc11ec22794dd8a3ed2c6aebe9bfe5
Rename time drift to time lag and expose to API
Introduce new fill mode behavior

--HG--
rename : web-animations/img/timed-item-states.svg => web-animations/img/timed-item-phases-and-states.svg