Give UI nodes with Display::None an empty clipping rect

[ickshonpe]

Objective

Outlines are drawn for UI nodes with Display::None set and their descendants. They should not be visible.

Solution

Make all Nodes with Display::None inherit an empty clipping rect, ensuring that the outlines are not visible.

Fixes #10940

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Changelog

• In update_clipping_system if a node has Display::None set, clip the entire node and all its descendants by replacing the inherited clip with a default rect (which is empty)

[alice-i-cecile]

Good comment, thanks!

[nicoburns]

Are there any performance implications to this "rendering and then clipping" as opposed to special casing Display::None eliding rendering entirely?

[ickshonpe]

Are there any performance implications to this "rendering and then clipping" as opposed to special casing Display::None eliding rendering entirely?

Basically what this PR does is special case Display::None in the clipping system to ellide rendering (if the intersection of an item's bounding rect and its clipping rect is empty then rendering is skipped).

Normally this is handled automatically because nodes with Display::None are given a zero size in the layout, but in the case of outlines they are drawn outside of the node's bounds so it doesn't help.