docs: fix various typos in reference docs

[Conduitry]

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This fixes some typos introduced in #13919 and adds a few words clarifying when it is that doubled would otherwise remain unchanged.

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[changeset-bot[bot]]

⚠️ No Changeset found

Latest commit: 5d063ed25af3ec18e25cb35cfd8b6ca5a424ca2b

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[pkg-pr-new[bot]]

pnpm add https://pkg.pr.new/svelte@14011

commit: 5d063ed

[Conduitry]

I've pushed some more typo fixes to other parts of the reference docs. Most of these should be fairly objective, but a few are stylistic.