Change `swift_library` `alwayslink` default to True

[brentleyjones]

This also changes the default for the swift_common.create_linking_context_from_compilation_outputs api.

SwiftPM works by linking all the .o files, and how .swift sources map to .o files can be dependent on the compiler options, so this should end up in a state that seem users familiar with SwiftPM/Xcode will expect.

Remove the private feature that was supporting this by honoring the objc flag.

PiperOrigin-RevId: 558766347 (cherry picked from commit https://github.com/bazelbuild/rules_swift/commit/c58d81a5fedcee78997dd085185d5744ad7d9e26)