feat(core): hasSlotted SSR hints

[bennypowers]

What I did

1. adds ssr-only ssr-hint-has-slotted="slotA,default,slotB" attribute to elements which use SlotController

Testing Instructions

1. view and verify results for pf-card.e2e.ts

Notes to Reviewers

1. Not entirely sure how best to document this, but i'm mostly certain I don't want to add this to individual element docs, but rather on a centralized ssr docs page

[changeset-bot]

⚠️ No Changeset found

Latest commit: f470aaa

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[github-actions]

✅ Commitlint tests passed!

More Info

{
  "valid": true,
  "errors": [],
  "warnings": [],
  "input": "feat(core): hasSlotted SSR hints"
}

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[github-actions]

SSR Test Run for 88b8804: Report

[github-actions]

SSR Test Run for 1d93145: Report

[github-actions]

SSR Test Run for 8f99c41: Report

[zeroedin]

just the one comment on the test, otherwise LGTM