fix: add webpack env data so that scripts can read it (like svelte-pr…

[farfromrefug]

…eprocessor)

This allows svelte-preprocessor to know many things but especially if we are building for ios/android

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• [ ] There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
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• [ ] Tests for the changes are included.

What is the current behavior?

What is the new behavior?

Fixes/Implements/Closes #[Issue Number].