bug: SSR merge_styles() don't handle correctly some style attributes

[adiguba]

Describe the bug

On SSR the style:directive use merge_styles() to merge the style attribute with the directives...

But it is too simplistic since it is based on a split(';'), and have some issues :

• It remove all duplicate properties, which can be problematic as it can be used for compatibility.
  (ex: "background-image:url(...); background-image: linear-gradient(...)")

• Comment are parsed and can be truncated in some case, which may generate an incorrect value.

• The ; inside quote or url() are used as split token, witch break the CSS property.

Note that this report mainly serves as a follow-up.
I currently work on a set_style() equivalent of #15352 that should handle theses cases.

Reproduction

https://www.sveltelab.dev/2jxwcou89yzclca

Logs

-

System Info

last version

Severity

annoyance