Turbopack: narrow async-module emptiness dependencies (#101154)
### What?
Adds `ModuleGraph::has_async_modules()`, a narrow turbo-tasks accessor
that reports whether the module graph contains any async module. The
browser and Node.js chunking code now use it when deciding whether to
include the async-module runtime helpers, instead of reading the full
`AsyncModulesInfo` set just to check whether it is empty.
### Why?
`AsyncModulesInfo` is a keyed cell holding every async module in the
graph. Awaiting the whole value makes the reading task depend on every
set member, so adding or removing an async module re-ran the
runtime/evaluate-chunk tasks even when the result could not change.
These callers only care about the empty/nonempty transition.
### How?
The accessor is a memoized task returning a boolean cell. The whole-set
read is isolated there; when the set membership changes but stays
nonempty, the accessor recomputes the same boolean and downstream
chunking tasks are not invalidated. Empty-to-nonempty and
nonempty-to-empty changes still invalidate consumers.
The existing runtime inclusion rules are unchanged, including the
shared-runtime short-circuits and always including the helpers for the
inline browser development runtime. The name follows the existing
async-module terminology because the set includes async externals, WASM
modules and transitive importers, not only modules with top-level await.
### Verification
- `cargo test -p turbopack-tests --test snapshot` (136 passed, no
snapshot changes; includes top-level-await and runtime snapshots)
- `cargo check -p turbopack-core -p turbopack-browser -p
turbopack-nodejs`
- `cargo clippy -p turbopack-core -p turbopack-browser -p
turbopack-nodejs`
- `cargo fmt --all -- --check`
- Temporary turbo-tasks invalidation harness (not committed): a boolean
emptiness accessor over a keyed set re-ran its consumer on
empty/nonempty transitions but not on nonempty membership changes; a
whole-set control consumer re-ran on each membership change.
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Co-authored-by: vercel-fleet-prod[bot] <318278635+vercel-fleet-prod[bot]@users.noreply.github.com>
Co-authored-by: Luke Sandberg <210140+lukesandberg@users.noreply.github.com>
