Fixed module-map resolution for external SwiftPM dependencies when .build/checkouts is symlinked

When building projects that use external SwiftPM dependencies, Tuist now emits -fmodule-map-file paths anchored to the absolute derived directory, instead of using $(SRCROOT)/../../tuist-derived/... paths that cross the symlinked .build/checkouts directory. Xcode 26.5’s dependency scanner resolves symlinks before traversing .. segments, which previously caused builds to fail with module map file... not found errors when CI caches symlinked checkouts. This change keeps the generated path inside tuist-derived/ and avoids the symlinked subtree, restoring builds in Xcode 26.5 with symlinked SwiftPM checkouts. Local projects are unaffected.