fix: remove DOM elements even if component creation fails

[mcous]

Overview

This PR fixes #190 by simplifying the caching strategy and ensuring the target div is added to the cache as soon as it's created, rather than after the component is rendered.

While working on this PR, I noticed a few inconsistencies with the render function's API, so I filed #312 and #313

Will keep this as a draft until I've smoke tested on my current app's suite

Change log

• Add target element to cache immediately
• Consolidate component creation and caching into renderComponent function
• Consolidate component destruction and target removal into cleanupComponent and cleanupTarget functions
• ~Remove component.$$.on_destroy usage~ I elected to keep this for strict backwards compatibility
  • $$.on_destroy was added in #54, which was a big rewrite about 5 years ago
  • Unfortunately I can't find any historical information about its intent. Perhaps @benmonro remembers?
  • It will not be possible in Svelte 5 as far as I can tell, and I think that's fine, because it's completely unnecessary if the user sticks to unmount and cleanup

[mcous]

Smoke tested by running on my company's ~1000 test suite, everything seemed to behave. Marking this one as ready for review, accordingly!

[mcous]

The changes in this PR have been merged into next. Gonna close this PR as unnecessary!