feat: support source and declaration maps in package

[JanNitschke]

Allows svelte-package to generate source and declaration maps from typescript and preprocessors. Updates the relative source paths of these maps when they are moved around during the build process.

closes #7793
closes #7792

#8843 fixes declaration maps paths when they are created.
My approach updates the path when files are copied, so it works with maps from any source.

This PR also generates .svelte.map files containing source maps for transformed svelte files, but I have not found a way to reference them from the generated .svelte file (see javascripts //# sourceMappingURL).

Svelte source maps are created based on compilerOptions.enableSourcemap in svelte.config.js which is true by default.

Typescript source maps and declaration maps respect the settings in tsconfig.json. This is different from declarations which are configured with the -t/--types flag. So maybe this should be changed.

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Latest commit: 7111a01

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@sveltejs/package	Minor

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[dummdidumm]

Thank you, and sorry for the very long delay in responding. I'm going to close this in favor of #8843 for now, because I'm not sure we should really expose source maps by default, because by default noone uploads their sources. In Svelte 5, source maps are always created, which would make matters worse, but at the same time Svelte 5 understands TypeScript types natively, so a big reason for preprocessors is gone, which means it's likely more people's Svelte components in the dist folder are actually the same as in the src folder.

That means we only really should be going forward with declaration source maps for now, hence merging #8843 instead and closing this. Thanks.