Support for static Swift modules

Allow static Swift libraries to be built, provide some way for a producing project to declare whether it should produce a shared library, static library, or both.

Dependency resolution selects a default linkage type when both are available. Allow a consumer to optionally declare which linkage variant to use.

Treat linkage as a variant dimension, and ensure all features from previous milestones work: For both linkage types, assemble and package binaries, install executables, assemble and run unit tests, publish to and resolve from Maven repository, import into IDE.

The issue names no files, tests, or entry points. Start by locating the existing native library linkage and variant handling for Swift, then trace how producing and consuming projects select linkage. Done means supporting static and shared variants across assembly, packaging, installation, unit tests, Maven publication and resolution, and IDE import.

Written by the indexing model from the issue text.