Instead of querying the index twice (once for up-to-date files, once for
outdated ones), collect file modification timestamps during the syntactic
scan phase and use them to filter a single semantic index query.
For files that don't support syntactic scans, use the semantic index
results even if outdated.
Also extracts symlink-aware mtime resolution into URL.fileModificationDate
and exposes snapshotHasInMemoryModifications(_:) on DocumentManager.
Rintaro Ishizaki
26f8efed5f