fix: take snippets into account when scoping css selectors

[dummdidumm]

This is an attempt to fix #10143
The CSS scoping logic is enhanced to take render tags into account - if one is found as the child of an element, we assume that the selector might match at runtime when combining the element(s) above the render tag and the element(s) inside the snippet. This doesn't do any advanced static analysis checks, so there can be false positives. I also notices that it's not enough to just check the current element for render tags, we need to do that recursively. I'm not sure I'm going down the right path doing this though, so I'm going to leave this as a draft for now for others that have worked in this code area before to take a look first.

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[trueadm]

@dummdidumm Is this PR still a WIP?

[dummdidumm]

Yeah still WIP, question still open - i'd leave it open and come back to it later

[dummdidumm]

Closing in favor of #13589