Add a noop index file to the main package

[thetarnav]

Should fix

solid-devtools import "solid-devtools"; is an entry point for the vite plugin.
If you're seeing this message you probably forgot to add the plugin to your vite config.

in prod builds

[changeset-bot]

🦋 Changeset detected

Latest commit: 3e93dba

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

This PR includes changesets to release 3 packages

Name	Type
solid-devtools	Patch
@solid-devtools/extension	Patch
@solid-devtools/overlay	Patch

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