anyrender_skia: respect CTM when blurring box shadows

[nicoburns]

Summary

draw_box_shadow created its blur MaskFilter with respect_ctm = false, so the blur sigma was interpreted in device pixels regardless of the canvas transform — on a HiDPI-scaled or CSS-transformed canvas, shadows blurred too little/too much. Flip it to true so the sigma is transformed by the CTM (matching Chrome's box-shadow behavior). This doesn't affect Skia's analytic blurred-rrect fast path.

Link to Devin session: https://dioxus.staging.devinenterprise.com/sessions/f10beda458004678a1c07c8b30d351ed
Requested by: @nicoburns

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