Auto merge of #26537 - mrobinson:backface, r=SimonSapin

layout_2020: Implement support for backface-visibility

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] There are tests for these changes

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tests/wpt/metadata-layout-2020/css/css-transforms/composited-under-rotateY-180deg-clip-perspective.html.ini

@@ -1,2 +0,0 @@
-[composited-under-rotateY-180deg-clip-perspective.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-transforms/composited-under-rotateY-180deg-clip.html.ini

@@ -1,2 +0,0 @@
-[composited-under-rotateY-180deg-clip.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-transforms/composited-under-rotateY-180deg.html.ini

@@ -1,2 +0,0 @@
-[composited-under-rotateY-180deg.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-transforms/rotateY-180deg-with-overflow-scroll.html.ini

@@ -1,2 +0,0 @@
-[rotateY-180deg-with-overflow-scroll.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-transforms/transform3d-backface-visibility-001.html.ini

@@ -1,2 +0,0 @@
-[transform3d-backface-visibility-001.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-transforms/transform3d-backface-visibility-002.html.ini

@@ -1,2 +0,0 @@
-[transform3d-backface-visibility-002.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-transforms/transform3d-backface-visibility-003.html.ini

@@ -1,2 +0,0 @@
-[transform3d-backface-visibility-003.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-transforms/transform3d-backface-visibility-004.html.ini

@@ -1,2 +0,0 @@
-[transform3d-backface-visibility-004.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-transforms/transform3d-backface-visibility-006.html.ini

@@ -1,2 +0,0 @@
-[transform3d-backface-visibility-006.html]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/css-transforms/transform3d-backface-visibility-007.html.ini

@@ -1,2 +0,0 @@
-[transform3d-backface-visibility-007.html]
-  expected: FAIL