move test `dom-element-scroll.html` from mozilla to wpt
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The test `dom-element-scroll.html` was originally landed on #19127.
It was designed for testing `scrollLeft` and `scrollTop`.
It is not only for servo. I thought I put a wrong place at that time. It should not be under `mozilla`. It's better placed under `wpt`.
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Use the color clip corresponding to the last background-image instead
of the last background-clip. (There may be more clips than images and
clips are repeated if there are less clips than images.)
Add a test.
Add an automatic test for border-image-outset with a gradient.
Convert two tests from UTF-8 LE with CRLF line endings to
UTF-8 with LF endings as the old files could not be viewed with servo.
Closes#16638
Move DL items from gfx to layout and implement corner clipping
Implement corner clipping.
Remove PixelFormat from WebrenderImageInfo.
Use WebRender text shadow.
Remove MallocSizeOf and Deserialize for DL items.
Closes#19649, closes#19680, closes#19802
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