perf(snapshot): dedupe JS sources between binary and v8 snapshot (#33992)
Files that were "lazy_loaded_js" but actually loaded during the snapshot
ended up in the binary twice - once in the V8 snapshot and again in the
rodata.
This PR collects which files were actually loaded during snapshotting,
and only retains the source for files that aren't in the snapshot
already.
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Co-authored-by: Bartek IwaĆczuk <biwanczuk@gmail.com>