Turbopack: expose list of non-inlined env vars (#95310)
Add a new method to `EcmascriptAnalyzable` to return the list of
non-inlined env vars
In this PR, this isn't used anywhere outside of the tests yet
While `cargo bench -p turbopack-ecmascript` does regress:
```
Benchmarking references/packages-bundle.js/full: Warming up for 1.0000 s
references/packages-bundle.js/full
time: [152.99 ms 153.34 ms 153.70 ms]
change: [+11.939% +12.678% +13.307%] (p = 0.00 < 0.05)
Performance has regressed.
Found 4 outliers among 100 measurements (4.00%)
4 (4.00%) high mild
Benchmarking references/packages-bundle.js/tracing: Warming up for 1.0000 s
references/packages-bundle.js/tracing
time: [153.07 ms 153.92 ms 155.15 ms]
change: [+34.997% +36.345% +37.554%] (p = 0.00 < 0.05)
Performance has regressed.
Found 4 outliers among 100 measurements (4.00%)
2 (2.00%) high mild
2 (2.00%) high severe
```
There is no measurable overall perf impact:
```
commit 7d29e358c8ac383a3019d552fd54f4d05645bf39 (HEAD, tag: v16.4.0-canary.5)
v16.4.0-canary.5
pnpm next build --experimental-build-mode=compil 400.89s user 51.96s system 747% cpu 1:00.61 total
pnpm next build --experimental-build-mode=compil 394.99s user 54.10s system 757% cpu 59.289 total
pnpm next build --experimental-build-mode=compil 399.87s user 58.71s system 772% cpu 59.398 total
```
vs
```
commit 9335597135118b8332b8e0d5a3bcedb596a3ef07 (HEAD -> mischnic/env-var-references)
remove runtime_all
pnpm next build --experimental-build-mode=compil 399.83s user 50.09s system 719% cpu 1:02.57 total
pnpm next build --experimental-build-mode=compil 403.57s user 53.79s system 743% cpu 1:01.52 total
pnpm next build --experimental-build-mode=compil 402.23s user 55.05s system 758% cpu 1:00.29 total
pnpm next build --experimental-build-mode=compil 400.17s user 55.15s system 761% cpu 59.817 total
```
