Package base settings stop clobbering SwiftPM target bundle identifiers

A package-wide PRODUCT_BUNDLE_IDENTIFIER template such as com.acme.$(PRODUCT_NAME) no longer overrides the per-target sanitized bundle identifier on generated SwiftPM targets. Underscore-prefixed modules that were previously broken (_RopeModule, _CollectionsUtilities, _NumericsShims, etc.) get valid CFBundleIdentifier values and build-for-testing works again. All other base settings, such as EXCLUDED_ARCHS, still propagate to targets and macros.