docs: desloppify browser support page (#18333)

The text in https://svelte.dev/docs/svelte/browser-support is quite
redundant and has a lot of AI smell. I did my best to make it more
concise and remove some slop comments in the generation script.

Requires a companion PR in svelte.dev:
https://github.com/sveltejs/svelte.dev/pull/2013

<img width="620" height="809" alt="image"
src="https://github.com/user-attachments/assets/7be9d5ff-1623-4897-a2d4-9a601b20f54d"
/>

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Co-authored-by: Rich Harris <rich.harris@vercel.com>