Make `swift_library` not generate an Objective-C header by default.
Make `swift_library` not generate an Objective-C header by default.

To generate a header, `generates_header` must be set to `True` on the target.

PiperOrigin-RevId: 367012879
(cherry picked from commit 413cc02802fff11916e5bf4738767f99cb1cf1e3)

bazelbuild/rules_swift,bazelbuild/rules_swift