Reverts "Copy gen_snapshots using python's shutil.copy, avoid links (#55830)" (#56034)

Reverts: #55830
Initiated by: chinmaygarde
Reason for reverting: Incremental builds are broken. flutter/flutter#157367
Original PR Author: aam

Reviewed By: {mraleph, cbracken}

This change reverts the following previous change:
Default implementation of copy does it via hardlink, which seems to be causing issues with Gatekeeper on mac.

BUG=flutter/flutter#154437

Author: auto-submit[bot]

ci/licenses_golden/excluded_files

@@ -436,7 +436,6 @@
 ../../../flutter/sky/packages/sky_engine/README.md
 ../../../flutter/sky/packages/sky_engine/lib/_embedder.yaml
 ../../../flutter/sky/packages/sky_engine/pubspec.yaml
-../../../flutter/sky/tools/cp.py
 ../../../flutter/sky/tools/create_embedder_framework.py
 ../../../flutter/sky/tools/create_ios_framework.py
 ../../../flutter/sky/tools/create_macos_binary.py

lib/snapshot/BUILD.gn

@@ -201,18 +201,12 @@ if (host_os == "mac" && (target_os == "mac" || target_os == "ios")) {
     gen_snapshot_target =
         "$dart_src/runtime/bin:$gen_snapshot_target_name($build_toolchain)"
 
-    action(target_name) {
-      script = "//flutter/sky/tools/cp.py"
-
+    copy(target_name) {
       # The toolchain-specific output directory. For cross-compiles, this is a
       # clang-x64 or clang-arm64 subdirectory of the top-level build directory.
       output_dir = get_label_info(gen_snapshot_target, "root_out_dir")
 
-      args = [
-        rebase_path("${output_dir}/${gen_snapshot_target_name}"),
-        rebase_path(
-            "${root_out_dir}/artifacts_$host_cpu/gen_snapshot_${target_cpu}"),
-      ]
+      sources = [ "${output_dir}/${gen_snapshot_target_name}" ]
       outputs =
           [ "${root_out_dir}/artifacts_$host_cpu/gen_snapshot_${target_cpu}" ]
       deps = [ gen_snapshot_target ]