Show async module scope in bundle analyzer (#98918)
### What?
Show source load scope in the bundle analyzer's single-build view: label
async-only and mixed sources in the table, mark them in the treemap with
a legend, and add an **Initial only** filter.
### Why?
Help distinguish sources reachable only behind an async import boundary
from sources reachable through an initial path (or both). This describes
**module-graph reachability**, not when a browser actually requests a
chunk.
### How?
Traverse the route's active-entry module graph, propagating initial,
async, and traced reachability across dependencies. Combine the reached
module scopes for each source, then pass the resulting classification to
the table, treemap, and filter. The new filter and indicators apply to
the single-build view; the comparison view keeps its existing behavior.
**Verification:** Bundle-analyzer typecheck, focused lint/format checks,
and production build passed; all eight combinations of the scope flags
were checked when simplifying the classification logic.
<!-- NEXT_JS_LLM -->
<!-- fleet d4ca0cb7-1e23-4f73-ac4e-5a6271239015 -->
---------
Co-authored-by: vercel-fleet-prod[bot] <318278635+vercel-fleet-prod[bot]@users.noreply.github.com>
Co-authored-by: Will Binns-Smith <755844+wbinnssmith@users.noreply.github.com>
