feat: add %sveltekit.version% placeholder for template interpolation

Allow app.html to interpolate the version string passed to kit.version.name in svelte.config.js. This makes it easier for static <head> includes for third-party scripts to be passed the current app version, e.g.

<script>
  GenericAnalytics.init({
    token: "abc123",
    application: "web",
    version: "%sveltekit.version%",
  });
</script>

This is nice ergonomic improvement, but there are several available workarounds:

set a variable using a globally included %sveltekit.head%
duplicate the version string to an env variable and use %sveltekit.env.PUBLIC_VERSION%
do your own pre-templating of app.html in hooks.server

This PR resolves https://github.com/sveltejs/kit/issues/12130.

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sveltejs / kit

feat: add %sveltekit.version% placeholder for template interpolation #12132

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

Tests

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