migrate to Oxc and Rolldown

Oxc is the future of SvelteKit and Vite, replacing esbuild which has been good for my/Gro's usage. Rolldown will handle the server and worker bundling cases but it's not ready yet. (edit: now in beta, https://rolldown.rs/)

One simple piece was completed in #518, replacing es-module-lexer with oxc-parser, but it got more complicated in #523

I opted for ts-blank-space for type stripping in #544 instead of oxc-transform, which is currently alpha and requires sourcemaps, but I think it's likely I'll make the switch when it has a beta/more stable release.

See all the esbuild_* files:

• esbuild_helpers.ts
• esbuild_plugin_external_worker.ts
• esbuild_plugin_svelte.test.ts
• esbuild_plugin_svelte.ts
• esbuild_plugin_sveltekit_local_imports.ts
• esbuild_plugin_sveltekit_shim_alias.ts
• esbuild_plugin_sveltekit_shim_app.ts
• esbuild_plugin_sveltekit_shim_env.ts

Start by reading src/lib/esbuild_helpers.ts and the other listed esbuild_* files to map the current bundling pieces. Run src/lib/esbuild_plugin_svelte.test.ts while comparing the Oxc and Rolldown constraints described in the issue. Done means the listed esbuild-based pieces have been migrated to Oxc and Rolldown where supported.