Allow vite.alias to be an array

[hgl]

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.

I'm not sure how to test this, would like to be enlightened.

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 pnpx changeset and following the prompts

[hgl]

What is this SyntaxError: Unexpected token '.' error? Tests passed on my local machine.

[benmccann]

It's because ?. doesn't work on Node 12

[hgl]

Thanks, fixed.