fix: store a persistent HMR wrapper per component

[dummdidumm]

The previous HMR logic created a new wrapper and source per HMR update, which meant things would either get wrapped more and more (prior to #12454) or would not get updated after the first update because the reference to the original would get lost (after #12454).

This fixes that by creating a registry within the HMR wrappers by filename are stored, retrieved and its signals updated. That way nothing gets lost, and nothing gets wrapped more than needed.

Fixes #12506

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[changeset-bot]

🦋 Changeset detected

Latest commit: a8c84f9

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

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[dummdidumm]

The runtime tests are failing because we're using the filename to check for pre-existing components, and the registry is preserved between tests and all tests have a main.svelte, and the rootDir option set in such a way that the resulting filenames are the same.

I don't know if that means we gotta adjust our registry key, or if we "just" need to have some HMR registry reset mechanism after each test

[Rich-Harris]

nearly broke my brain but i think i figured it out #12547

[Rich-Harris]

merged #12547, so will close this