feat: enable prebundling by default

[dominikg]

enable prebundleSvelteLibraries by default

TODO:

• merge fix: preserve reincludes of excluded with prebundleSvelteLibraries #493
• release vite-plugin-svelte patch so a fixed version with default disabled exists in the registry
• add logging for prebundling stats and dev ssr compile time to increase visibility for page load time issues during dev
• add documentation about tradeoffs for prebundling, deep imports vs index imports, build and ssr.
• merge this PR and release vite-plugin-svelte minor
• remove inline setting of prebundleSvelteLibraries: true from kit and bump it's minimum v-p-s version

[dominikg]

The guides and recommendations likely have to be rewritten as there are several factors at play.

A) optimizeDeps currently does not work for ssr, leading to slow load times during dev when you import a large library without using deep imports
B) using a preprocessor that rewrites imports from index import to deep import causes a massive problem and must be avoided when prebundling is enabled for that library ( eg carbon-preprocess-svelte optimizeImports preprocessor )
C) index imports still have an effect on build time. All components exported from an index have to be compiled, even if your Application only uses a few.

There is no golden rule for what's right, just general recommendations:

1. don't use an import rewriting preprocessor together with prebundleSvelteLibraries
2. deep imports avoid compiling unused .svelte files which can speed up dev ssr and build times esp. for large libraries
3. index imports provide a better DX by enabling autocomplete even for previously unused components

picking between 2 and 3 has to be done by the users, v-p-s cannot decide that.

To improve performance for index imports we can look into enabling optimizeDeps for build and ssr too, but unfortunately i havn't been able to get it running for ssr so far.

[bluwy]

The docs are organized well for me. Have some nits below: