fix: configure Vite config optimizeDeps.entries option

[eltigerchino]

fixes #11793

We need to specify optimizeDeps.entries for the Vite config to scan for dependencies that should be optimised because we have set rollupOptions.build.input and that overrides Vite's default scanning behaviour. This prevents the excessive Vite dependency optimisation and reloading on page navigation during development when it discovers dependencies used by the page.

Note that this PR merges the optimizeDeps.entries specified by the user's Vite configuration instead of overriding it. We considered just adding these to the Vite user config so it's more visible but there's no way to retrieve the dynamic path of the Kit routes folder and hook file names which are configurable in svelte.config.js.

Additional context from the maintainer's Discord chat.

---

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

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with pnpm test and lint the project with pnpm lint and pnpm check

Changesets

• If your PR makes a change that should be noted in one or more packages' changelogs, generate a changeset by running pnpm changeset and following the prompts. Changesets that add features should be minor and those that fix bugs should be patch. Please prefix changeset messages with feat:, fix:, or chore:.

Edits

• Please ensure that 'Allow edits from maintainers' is checked. PRs without this option may be closed.

[changeset-bot]

🦋 Changeset detected

Latest commit: d61d3f0

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

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[dominikg]

great to see the added test working 👍