fix: populate globalThis with defines in Vitest

[elliott-with-the-longest-name-on-github]

Closes #16214

Sets defines on globalThis when we detect that Vitest is running, since it "helpfully" deletes them for us.

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from be586f3:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/be586f39b6461f43cd834d272782d5491dfcf704

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16224

[changeset-bot]

🦋 Changeset detected

Latest commit: be586f3

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

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[elliott-with-the-longest-name-on-github]

@MaddyGuthridge can you install using the pkg.svelte.dev link above and let me know if it fixes your issue? I think it should...

[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-16224-svelte.vercel.app/

[MaddyGuthridge]

I'll give this a go after work today

[MaddyGuthridge]

I've tried it out, but had some issues:

• This change targets v3 of svelte-kit, which means there are other breaking changes, none of which appear in the mainline documentation yet. Is a backport to the v2 branch possible?
• The JSON error mentioned by the vercel bot.

$ npm t
> kit-template-default@0.0.1 test
> vitest run


⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ Startup Error ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯
SyntaxError: Unexpected token 'g', "globalThis"... is not valid JSON
    at JSON.parse (<anonymous>)
    at BasicMinimalPluginContext.handler (file:///home/maddy/Downloads/sveltejs-kit-template-default-fann5ee8/node_modules/@sveltejs/kit/src/exports/vite/index.js:506:67)
    at async runConfigHook (file:///home/maddy/Downloads/sveltejs-kit-template-default-fann5ee8/node_modules/vite/dist/node/chunks/node.js:35760:15)
    at async resolveConfig (file:///home/maddy/Downloads/sveltejs-kit-template-default-fann5ee8/node_modules/vite/dist/node/chunks/node.js:35195:11)
    at async _createServer (file:///home/maddy/Downloads/sveltejs-kit-template-default-fann5ee8/node_modules/vite/dist/node/chunks/node.js:25332:65)
    at async createViteServer (file:///home/maddy/Downloads/sveltejs-kit-template-default-fann5ee8/node_modules/vitest/dist/chunks/cli-api.24X8XwN1.js:8835:17)
    at async createVitest (file:///home/maddy/Downloads/sveltejs-kit-template-default-fann5ee8/node_modules/vitest/dist/chunks/cli-api.24X8XwN1.js:14221:18)
    at async prepareVitest (file:///home/maddy/Downloads/sveltejs-kit-template-default-fann5ee8/node_modules/vitest/dist/chunks/cli-api.24X8XwN1.js:14588:14)
    at async startVitest (file:///home/maddy/Downloads/sveltejs-kit-template-default-fann5ee8/node_modules/vitest/dist/chunks/cli-api.24X8XwN1.js:14531:14)
    at async start (file:///home/maddy/Downloads/sveltejs-kit-template-default-fann5ee8/node_modules/vitest/dist/chunks/cac.D3xHeqeL.js:2340:15)

[dummdidumm]

this should target main (I briefly tried through the UI but that will try to add all of version-3, too), otherwise lgtm