LibWeb: Support `x` and `y` attributes on nested SVGs

[MacDue]

This allows positioning a child SVG relative to its parent SVG.

Note: These have been implemented as CSS properties as in SVG 2, these are geometry properties that can be used in CSS (see https://www.w3.org/TR/SVG/geometry.html), but there is not much browser support for this. It is nicer to implement than the ad-hoc SVG attribute parsing though, so I feel it may make sense to port the rest of the attributes specified here (which should fix some issues with viewport relative sizes).

This fixes the logo position on the Azure pipelines badge: