fix: avoid inlining optimizer hidden sourcemaps (fix #23287)

[szupzj18]

Root cause

The dependency optimizer emits hidden source maps, but optimized dependencies were sent through the normal transform response path. send() therefore converted the returned map into an inline data URL, making the HTTP response much larger than the optimized file on disk.

Change

Serve optimized dependencies with an external sourceMappingURL that keeps the browser hash query, and return the post-transform map from the dedicated .map endpoint. This avoids base64 response bloat while preserving debugger mappings and existing path-traversal sanitization.

Validation

• Added a RED/GREEN regression proving the optimized response uses an external map and its .map endpoint serves the generated map
• pnpm test-unit packages/vite/src/node/__tests__/optimizer/hiddenSourcemap.spec.ts packages/vite/src/node/__tests__/optimizer/customExtensionBundleClose.spec.ts
• pnpm run test-serve js-sourcemap (9 passed)
• pnpm exec oxfmt --check ...
• pnpm exec eslint ...
• pnpm run build

Fixes #23287