When displaying SVGs inside a navigable directly, we want to display
them in the size specified by their width and height attributes instead
of stretching them to the viewport as layout normally would.
However, when doing so, we need to actually check that the SVG we are
laying out is indeed directly inside the navigable. Otherwise we just
blindly overwrite whatever content sizes have been calculated by layout
code for e.g. SVG elements inlined somewhere in an HTML document.
Due to the way this was written originally, the bug was not very
noticable. The code overwrote the content width/height with the computed
width/height, which was often still correct in the sense that those two
had the same value. However, content size may also be the result of
{min,max}-{width,height} constraints, which can make it differ from the
computed values.
This bug was likely a regression introduced in
f5e01192cc.
Special handling for SVGClipPathElement and SVGMaskElement, which use a
a ViewBox and PreserveAspectRatio value internally, has been moved to
`SVGFormattingContext`.
This ensures that percentages resolve against the foreignObject's size
instead of the size of its containing block.
This makes user profile pictures clip correctly in the "Friends" view
of the Discord app.
This is according to the default user-agent style from the SVG2 spec.
In order for this to work correctly, we also have to assign width and
height to foreignObject boxes during SVG layout, since they are handled
manually by SVGFormattingContext.
