fix: trim whitespace while migrating blocks

[paoloricciuti]

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This kinda closes #13933...since now having no whitespace before the blocks is enforced by svelte let's trim everything while migrating.

Edit this will also close #13483 (we can't really fix the inconsistencies without a breaking change unfortunately)

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[changeset-bot]

🦋 Changeset detected

Latest commit: 56f78fc

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

This PR includes changesets to release 1 package

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svelte	Patch

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[pkg-pr-new]

pnpm add https://pkg.pr.new/svelte@13941

commit: 56f78fc

[trueadm]

Why does it "kinda close", what's missing?

[paoloricciuti]

Why does it "kinda close", what's missing?

It can be closed, is just not the thing they asked for 😄