feat: Add slots to allow customizing AccordionItem open/close icons

[bshore]

Linked Issue

N/A - Discussed in Discord #contributors channel.

Description

Adds two optional slots for customizing the AccordionItem icon when open or closed.

• iconClosed - What to display when the given AccordionItem is closed.
• iconOpen - What to display when the given AccordionItem is open.

Updated the component documentation page with a showcase + code example.

Preview Link

Changsets

Instructions: Changesets automate our changelog. If you modify files in /packages, run pnpm changeset in the root of the monorepo, follow the prompts, then commit the markdown file. Changes that add features should be minor while chores and bugfixes should be patch. Please prefix the changeset message with feat:, bugfix: or chore:.

Checklist

Please read and apply all contribution requirements.

• This PR targets the dev branch (NEVER master)
• Documentation reflects all relevant changes
• Branch is prefixed with: docs/, feat/, chore/, bugfix/
• Ensure Svelte and Typescript linting is current - run pnpm ci:check
• Ensure Prettier linting is current - run pnpm format
• All test cases are passing - run pnpm test
• Includes a changeset (if relevant; see above)

[changeset-bot]

🦋 Changeset detected

Latest commit: b178e0b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@skeletonlabs/skeleton	Minor

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Name	Status	Preview	Updated (UTC)
skeleton-docs	✅ Ready (Inspect)	Visit Preview	Dec 18, 2023 9:55pm

[endigo9740]

@bshore one minor issue noted above - FYI I'm currently limited to running PR audits on weekends, so expect a deeper review later this week. Thanks!

[endigo9740]

@bshore I've made a few notable modifications:

1. I updated the changeset to remove a reference to the Skeleton Docs. We don't keep a changelog for the docs.
2. I've made a number of refactors to reduce the amount of code, while also preserving backwards compatibility
3. Namely we allowed folks to customize the built-in caret icon rotation - so we need to continue to support that
4. When a custom icon slot is provided it then renderings a different UI for handling this (which doesn't rotate)
5. I've added a FIXME comment for a region prop we'll need to update in our next major release.
6. We opt for minimal examples in our docs, so I've updated the doc example accordingly.

I'm still not fond of having to update the icons per item, but well chalk that up to a Svelte v4 limitation and plan to revisit for our Svelte v5 rewrite coming soon!

Overall, great job. We appreciate your contribution!