fix: skip fallback sourcemap generation for ?raw imports

[semimikoh]

Summary

Skip dev-server fallback sourcemap generation for ?raw imports.

?raw responses already embed the full source text in the generated JS module. Injecting an additional fallback inline sourcemap
duplicates that content and can lead to severe memory amplification for large newline-heavy files.

This change keeps ?raw import behavior intact, but disables fallback sourcemap injection for raw requests only.

Changes

• add skipFallbackSourcemap support to send()
• pass skipFallbackSourcemap: true for ?raw requests in transform middleware
• add regression tests for normal fallback sourcemap injection and the raw-import skip case

Why

The reported OOM happens in the dev-server fallback sourcemap path rather than in the raw file read alone. This is a narrow fix that
avoids changing ?raw semantics while removing the highest-cost duplication path.

Validation

• pnpm exec eslint packages/vite/src/node/server/send.ts packages/vite/src/node/server/middlewares/transform.ts packages/vite/src/node/ server/__tests__/send.spec.ts
• pnpm exec tsc -p packages/vite/src/node/tsconfig.json --noEmit
• pnpm exec vitest run packages/vite/src/node/server/__tests__/send.spec.ts packages/vite/src/node/server/__tests__/ transformRequest.spec.ts

Fixes part of #22132

[bluwy]

What if we fix it this way?

vite/packages/vite/src/node/plugins/asset.ts

Lines 208 to 213 in 6e585dc

	return {
	code: `export default ${JSON.stringify(
	await fsp.readFile(file, 'utf-8'),
	)}`,
	moduleType: 'js', // NOTE: needs to be set to avoid double `export default` in `?raw&.txt`s
	}

We can add map: { mappings: '' } so that we generate an empty sourcemap on behalf, then later send.ts won't generate a sourcemap for it.

Honestly, I still think generating a fallback sourcemap in general doesn't make sense at all, but this could be an easy workaround for now. ref #13514. cc @sapphi-red

[sapphi-red]

What if we fix it this way?
[code block]
We can add map: { mappings: '' } so that we generate an empty sourcemap on behalf, then later send.ts won't generate a sourcemap for it.

That sounds better to me.

[semimikoh]

@bluwy @sapphi-red Updated to emit map: { mappings: '' } from the asset plugin instead of adding skipFallbackSourcemap flag.