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

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

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@sveltejs/package	Minor

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