`<use>` elements don't work in SVG costumes (and the Rays backdrop)

[nimeratus]

Expected Behavior

Those <use> elements that reference an element inside the costume are rendered normally

Actual Behavior

All <use> elements are removed

This prevents the Rays backdrop from showing up, because it has a clip path with a <use> element applied to everything (https://scratch.mit.edu/discuss/topic/842302/)

It also prevents the dropdown arrows and the pen icon in scratchblocks SVGs from showing up

Steps to Reproduce

Steps to reproduce the behavior:

1. Go to 'https://scratch.mit.edu/projects/editor/'
2. Add the 'Rays' backdrop
3. The backrop appears in the Stage thumbnail, but not on the stage canvas because the <use> element is removed

System Details

• Windows 10, Chrome 141

from https://scratch.mit.edu/discuss/topic/842302/:

• ChromeOS 14541, Chrome 138
• Windows 7, Chrome 139
• Windows 7, Chrome 109

Screenshots

[scratching-claws]

I think this could be related to the recent SVG sanitation: #269