Stop false duplicate xcframework warnings for external SwiftPM products

Running tuist generate no longer warns about a “duplicate xcframework dependency” when the same precompiled .xcframework is reached through multiple external SwiftPM products. The mapper now collapses identical .xcframework entries produced by external expansion into a single graph dependency, so linting matches what generation writes to the project. Duplicates that you declare explicitly in a ProjectDescription manifest are still detected and still trigger the warning.