perf: use magic-string hires boundary for sourcemaps

[bluwy]

Description

Generate sourcemap segments per word boundary instead of per character. Rich-Harris/magic-string#255

I didn't test this a lot but I think everything should stay the same. We're using magic-string to manipulate JS and CSS, which are code that are semantically separated by word boundaries.

Additional context

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the PR Title Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[stackblitz]

Run & review this pull request in StackBlitz Codeflow.

[patak-dev]

Awesome work! Tempted to release this one in a patch, but it is probably better to merge it in the Vite 5 beta.

@bmeurer maybe you could help us check this one out?

[bluwy]

I ran the benchmark at https://github.com/vitejs/vite-benchmark/actions/runs/5689588084 and it doesn't seem to affect performance, so maybe it only helps a bit or the benchmark fixtures aren't generating many sourcemaps.

[sapphi-red]

Awesome that you implemented this! @bmeurer suggested a similar way a bit ago (#13514 (comment)) to me.

I ran the benchmark at https://github.com/vitejs/vite-benchmark/actions/runs/5689588084 and it doesn't seem to affect performance, so maybe it only helps a bit or the benchmark fixtures aren't generating many sourcemaps.

I guess that's because vitejs/vite-benchmark doesn't run benchmarks for build.

[bluwy]

Awesome work! Tempted to release this one in a patch, but it is probably better to merge it in the Vite 5 beta.

I think it should be rather safe to merge this one. It shouldn't degrade the sourcemap when using it.

[patak-dev]

Ok, let's try it out

[bmeurer]

Nice one, thanks!

This might be interesting to bring up with the TC39-TG4 in the context of source map standardization. cc @jaro-sevcik @littledan