Turbopack: properly remove unused TS enums with scope hoisting (#88205)
Needs https://github.com/swc-project/swc/pull/11777
https://github.com/swc-project/swc/pull/10560 added `Files.map_raw_pos` which can be used to translate BytePos before generating the sourcemap.
The same is also needed in `SourceMapper`, so that the `pos.is_pure()` in `emit_leading_comments` uses the decoded BytePos.
This came up in https://github.com/vercel/next.js/pull/88205 where my BytePos re-encoding mechanism caused `BytePos::PURE` to not codegen the pure comment anymore.
Closes https://github.com/vercel/next.js/issues/88009
Closes https://github.com/vercel/next.js/pull/90004
Closes PACK-6424