[macOS][iOS] Eliminate strip_bitcode action (flutter#36627)

Eliminates the `strip_bitcode` GN rule defined in
//flutter/sky/tools/mac.gni and the related script at
//flutter/sky/tools/strip_bitcode.py.

As of Xcode 14, bitcode is deprecated, no longer enabled by default, and
generates a warning message if a project enables it. Bitcode support
will be removed entirely from a future version of Xcode.

The `strip_bitcode` rule had two purposes:
1. Copy the binary specified by its input parameter to the path
   specified by its output parameter.
2. Strip bitcode segments as it does so.

While we no longer require the second of these functions, we still use
the first to create a `gen_snapshot` binary suffixed with the target
architecture. This replaces `strip_bitcode` with the built-in gn `copy`
rule instead.

Issue: flutter/flutter#107884
Issue: flutter/flutter#112896
Issue: flutter/flutter#101138
Issue: flutter/flutter#103386

lib/snapshot/BUILD.gn

@@ -6,7 +6,6 @@ import("//build/compiled_action.gni")
 import("//build/fuchsia/sdk.gni")
 import("//flutter/common/config.gni")
 import("//flutter/lib/ui/dart_ui.gni")
-import("//flutter/sky/tools/macos.gni")
 import("//third_party/dart/utils/compile_platform.gni")
 
 # Generates the Dart/Flutter core platform files and tools.
@@ -252,7 +251,7 @@ bin_to_linkable("platform_strong_dill_linkable") {
 # This target is used for builds targeting iOS/Android OS.
 if (host_os == "mac" && target_os != "mac" &&
     (target_cpu == "arm" || target_cpu == "arm64")) {
-  strip_bitcode("create_arm_gen_snapshot") {
+  copy("create_arm_gen_snapshot") {
     # The toolchain-specific output directory. For cross-compiles, this is a
     # clang-x64 or clang-arm64 subdirectory of the top-level build directory.
     host_output_dir = get_label_info(
@@ -265,8 +264,8 @@ if (host_os == "mac" && target_os != "mac" &&
       target_cpu_suffix = "armv7"
     }
 
-    input = "${host_output_dir}/gen_snapshot"
-    output = "${host_output_dir}/gen_snapshot_${target_cpu_suffix}"
+    sources = [ "${host_output_dir}/gen_snapshot" ]
+    outputs = [ "${host_output_dir}/gen_snapshot_${target_cpu_suffix}" ]
     deps = [ "//third_party/dart/runtime/bin:gen_snapshot($host_toolchain)" ]
     visibility = [ ":*" ]
   }
@@ -280,15 +279,15 @@ if (host_os == "mac" && target_os != "mac" &&
 #
 # This target is used for builds targeting macOS.
 if (host_os == "mac" && target_os == "mac") {
-  strip_bitcode("create_macos_gen_snapshots") {
+  copy("create_macos_gen_snapshots") {
     # The toolchain-specific output directory. For cross-compiles, this is a
     # clang-x64 or clang-arm64 subdirectory of the top-level build directory.
     host_output_dir = get_label_info(
             "//third_party/dart/runtime/bin:gen_snapshot($host_toolchain)",
             "root_out_dir")
 
-    input = "${host_output_dir}/gen_snapshot"
-    output = "${root_out_dir}/gen_snapshot_${target_cpu}"
+    sources = [ "${host_output_dir}/gen_snapshot" ]
+    outputs = [ "${root_out_dir}/gen_snapshot_${target_cpu}" ]
     deps = [ "//third_party/dart/runtime/bin:gen_snapshot($host_toolchain)" ]
     metadata = {
       snapshot_entitlement_file_path = [ "gen_snapshot_{$target_cpu}" ]