Auto merge of #18210 - mantaroh:clip-interpolation-fix, r=nox

Skip adding/accumulating ClipRect values which corresponding rect offset is auto.

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This is a PR for https://bugzilla.mozilla.org/show_bug.cgi?id=1390352

This patch will skip adding/accumulating the values which corresponding rect offset is auto, and  make Servo_AnimationValues_ComputeDistance return negative value instead of 0.0 when the function fails to distinguish its failure.

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- [X] `./mach test-tidy` does not report any errors

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There are already these tests in dom/smil/tests of gecko, this PR will enable these tests.
For detail, see https://bugzilla.mozilla.org/show_bug.cgi?id=1390352.

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