Fix extension_safe attr not passing copts

[luispadron]

When using extension_safe the copt for the objc/swift library must also supply -fapplication-extension/-application-extension

[luispadron]

Use += here instead of append so that select is supported.

[jszumski]

Thanks to this test for the help!

assert_xcconfig(
    name = "only_used_as_condition",
    xcconfig = {"APPLICATION_EXTENSION_API_ONLY": "YES"},
    expected = {"linkopts": ["-fapplication-extension", "-fapplication-extension"], "objc_copts": ["-fapplication-extension"], "swift_copts": ["-application-extension"]},
),

[luispadron]

Updated one of the examples, without this change it fails with:

tests/ios/frameworks/dynamic/b/lib.swift:11:15: error: 'accessoryCircular' is only available in iOS 16.0 or newer
            [.accessoryCircular]
              ^

so should catch regressions in the future too