fix: adjust loc property of Program nodes created from <script> elements

[Rich-Harris]

This adjusts the loc of the instance/module Program to correspond to the inside of the <script> tag, rather than always being 0. Though I've just realised that this won't actually fix the related issue (#17003) because the problem is the end rather than the start — may need to come up with a different solution. Fixes #17003

The nub of the problem is this — we're setting the bounds of the default-export function body to the bounds of the instance Program so that comments are inserted correctly:

svelte/packages/svelte/src/compiler/phases/3-transform/client/transform-client.js

Lines 401 to 402 in 1482ae8

	// trick esrap into including comments
	component_block.loc = instance.loc;

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Latest commit: 9fa846e

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Playground

pnpm add https://pkg.pr.new/svelte@17428

[dominikg]

ran the tests that were failing in vite-plugin-svelte with vite8 using this PR and they passed. 🥳

do you want to merge #17167 after this as well or close it?