src: stop copying code cache #47144

The code cache is quite large - around 1.3 MiB. Change the code to use non-owning buffers to avoid copying it. For starting up an otherwise empty main isolate, this saves around 1.3 MiB of unique set size memory (9.9 MiB -> 8.6 MiB) and 1.1ms elapsed time (22.9 ms -> 21.8 ms). Copying the code cache is unnecessary since: 1. for the builtin snapshot, the code cache data has static lifetime. 2. for non-builtin snapshots, we create copies of the code cache data in `SnapshotDeserializer::ReadVector`. These copies are owned by the `Environment` (through `IsolateData` -> `SnapshotData`), so they won't be deallocated. 3. a worker thread can copy a parent's isolate's code cache, but in that case we still know that the parent isolate will outlive the worker isolate. (Admittedly point (2) feels a little fragile from a lifetime perspective, and I would be happy to restrict this optimization to the builtin snapshot.) ```console $ perf stat -r 100 -e ... ./node -e 0 Performance counter stats for './node -e 0' (100 runs): 21.78 msec task-clock 2760 page-faults 113161604 instructions 18437648 branches 423230 branch-misses 853093 cache-references 41474 cache-misses 0.0225473 +- 0.0000504 seconds time elapsed ( +- 0.22% ) $ perf stat -r 100 -e ... ./node-main -e 0 Performance counter stats for './node-main -e 0' (100 runs): 22.91 msec task-clock 3102 page-faults 114890673 instructions 18751329 branches 428909 branch-misses 895721 cache-references 45202 cache-misses 0.0233760 +- 0.0000741 seconds time elapsed ( +- 0.32% ) ```

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src: stop copying code cache #47144

src: stop copying code cache #47144

Commits on Apr 10, 2023