Auto merge of #18036 - birtles:reject-easing-lists, r=hiro
Auto merge of #18036 - birtles:reject-easing-lists, r=hiro

Reject easings with trailing content in Servo_ParseEasing

Servo side changes for [Gecko bug 1385141](https://bugzilla.mozilla.org/show_bug.cgi?id=1385141).

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