Fix or selectively silence warnings in src/components.
Merge pull request #2787 from SimonSapin/warnings

Fix or selectively silence warnings in src/components.
Add initial LogicalSize and LogicalPoint geometry, for CSS Writing Modes.
Account for the container height when converting a point

... in case the inline direction is bottom to top.

Gecko does not do this since (I’m told) they do not support
vertical RTL nor sideways-left yet.
Logical geometry: remove trivial accessors and make fields public.
Add LogicalMargin, the flow-relative dimension equivalent to SideOffsets2D.
Add LogicalRect, the flow-relative dimension rectangle.
Implement Eq, Clone, Show, and is_zero() on logical geometry stuff.
WIP
WIP²
WIP³