Support lazy fallback in <Show>

[marvinhagemeister]

Add support for lazily instantiating the fallback of <Show>:

<Show
  when={toggle}
  fallback={() => <p>I'm lazy</p>}
>
  <p>foo</p>
</Show>

This avoids eager evaluation of whatever is passed to fallback. For signal based code you might only want to access signals in the fallback case for example.

[changeset-bot]

🦋 Changeset detected

Latest commit: 6b051b5

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

This PR includes changesets to release 3 packages

Name	Type
@preact/signals	Minor
@preact/signals-react	Minor
preact-signals-devtools	Patch

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[github-actions]

Size Change: +17 B (+0.01%)

Total Size: 188 kB

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docs/dist/assets/bench-********.js	1.6 kB	-1 B (-0.06%)
docs/dist/assets/devtools-********.js	911 B	+2 B (+0.22%)
docs/dist/assets/index-********.js	8.43 kB	+3 B (+0.04%)
docs/dist/assets/utils.module-********.js	516 B	+13 B (+2.58%)

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packages/devtools-ui/dist/devtools-ui.mjs	15.6 kB
packages/preact-transform/dist/signals-transform.js	1.3 kB
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packages/preact-transform/dist/signals-transform.umd.js	1.42 kB
packages/preact/dist/signals.js	1.81 kB
packages/preact/dist/signals.mjs	1.74 kB
packages/react-transform/dist/signals-transform.js	7.28 kB
packages/react-transform/dist/signals-transform.mjs	6.47 kB
packages/react-transform/dist/signals-transform.umd.js	7.39 kB
packages/react/dist/signals.js	214 B
packages/react/dist/signals.mjs	165 B
packages/vite-plugin/dist/vite-plugin.js	8.86 kB
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