addUneditedChunk consumes too much memory

[hackwaly]

It seems rawSegments.push segments char by char.

vscode-profile-2022-06-23-00-15-42.heapprofile.zip

[FeldrinH]

According to https://github.com/Rich-Harris/magic-string#sgeneratemap-options- this appears to be intended behavior with hires: true. However, in vitejs/vite#11745, using this does seem to be the cause of a signifficant increase in memory usage.