Un-conditionalize logic for features that require Xcode 15.0 or higher (dropping support for Xcode 14)

[luispadron]

PiperOrigin-RevId: 640116533

Cherry picks: f235362

Submitting to the App Store requires Xcode 15+ so this cherry pick (and some other changes to < Xcode 15 logic I made) drops support for Xcodes less than 15

[luispadron]

Seems like a last_green issue, unrelated to this for doc tests:

ERROR: /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/ec321eb2cc2d0f8f91b676b6d4c66c29/external/rules_java/toolchains/BUILD: no such target '@@rules_java//toolchains:bootstrap_runtime_toolchain_type': target 'bootstrap_runtime_toolchain_type' not declared in package 'toolchains' defined by /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/ec321eb2cc2d0f8f91b676b6d4c66c29/external/rules_java/toolchains/BUILD
--
  | (23:55:06) ERROR: /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/ec321eb2cc2d0f8f91b676b6d4c66c29/external/remote_jdk8_macos_aarch64_toolchain_config_repo/BUILD.bazel:27:10: no such target '@@rules_java//toolchains:bootstrap_runtime_toolchain_type': target 'bootstrap_runtime_toolchain_type' not declared in package 'toolchains' defined by /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/ec321eb2cc2d0f8f91b676b6d4c66c29/external/rules_java/toolchains/BUILD and referenced by '@@remote_jdk8_macos_aarch64_toolchain_config_repo//:bootstrap_runtime_toolchain'
  | (23:55:06) ERROR: /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/ec321eb2cc2d0f8f91b676b6d4c66c29/external/io_bazel_stardoc/src/main/java/com/google/devtools/build/skydoc/renderer/BUILD:17:12: Analysis failed
  | (23:55:06) ERROR: Analysis of target '//doc:test_api' failed; build aborted: Analysis failed