chore: replace cross-env with pnpm shell emulator

[teemingc]

This PR removes cross-env in favour of pnpm's shellEmulator which "just works". We're currently using this in the svelte, kit, and svelte.dev repositories too.

https://pnpm.io/settings#shellemulator

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[teemingc]

Specifying the pnpm run command fixes an endless recursion because it didn't exclude the root workspace test command.
See https://pnpm.io/cli/recursive

[jasonlyu123]

The test failure should be due to the magic-string update in svelte2tsx.

[teemingc]

The test failure should be due to the magic-string update in svelte2tsx.

Thanks for sharing. I've been wondering why removing cross-env would cause those tests to fail 😅