Auto merge of #20420 - pyfisch:corner-clipping, r=emilio

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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components/layout/construct.rs

@@ -17,6 +17,7 @@ use ServoArc;
 use block::BlockFlow;
 use context::{LayoutContext, with_thread_local_font_context};
 use data::{LayoutDataFlags, LayoutData};
+use display_list::items::OpaqueNode;
 use flex::FlexFlow;
 use floats::FloatKind;
 use flow::{AbsoluteDescendants, Flow, FlowClass, GetBaseFlow, ImmutableFlowUtils};
@@ -27,7 +28,6 @@ use fragment::{Fragment, GeneratedContentInfo, IframeFragmentInfo, FragmentFlags
 use fragment::{InlineAbsoluteHypotheticalFragmentInfo, TableColumnFragmentInfo};
 use fragment::{InlineBlockFragmentInfo, SpecificFragmentInfo, UnscannedTextFragmentInfo};
 use fragment::WhitespaceStrippingResult;
-use gfx::display_list::OpaqueNode;
 use inline::{InlineFlow, InlineFragmentNodeInfo, InlineFragmentNodeFlags};
 use linked_list::prepend_from;
 use list_item::{ListItemFlow, ListStyleTypeContent};