Reverts "[macOS] Generate universal gen_snapshots (flutter#52885)" (flutter#52913)

Reverts: flutter/engine#52885
Initiated by: cbracken
Reason for reverting: while this patch worked fine, it pushed the mac build bot over its time limit. Previous builds were just squeaking under the wire but seeing timeouts on the mac_host_engine host_release shard after this commit. e.g. https://ci.chromium.org/ui/p/flutter/builders/prod/Mac%20mac_host_engine/10667/overview

Looking at ci.yaml I see the timeout is set to 240, but the timeout on the failing shard is c
Original PR Author: cbracken

Reviewed By: {jmagman}

This change reverts the following previous change:
Previously, the `gen_snapshot_arm64` and `gen_snapshot_x64` binaries used by the tool were all built for x64 architecture. As such, developers building apps with Flutter rely on Rosetta translation with every build.

This refactors the gen_snapshot build rules on macOS hosts to consistently produce `gen_snapshot_arm64` and `gen_snapshot_x64` binaries with the target architecture of the build but with as universal binaries with both host architectures.

### arm64 host build

Prior to this patch we emitted:
* gen_snapshot_arm64 (arch: x64, target_arch: simarm64)

After this patch, we emit:
* artifacts_x64/gen_snapshot_arm64 (arch: x64, target_arch: simarm64)
* artifacts_arm64/gen_snapshot_arm64 (arch: arm64, target_arch: arm64)
* gen_snapshot_arm64 (universal binary composed of both of the above)

### x64 host build

Prior to this patch we emitted:
* gen_snapshot_x64 (arch: x64, target_arch: x64)

After this patch, we emit:
* artifacts_x64/gen_snapshot_x64 (arch: x64, target_arch: x64)
* artifacts_arm64/gen_snapshot_x64 (arch: arm64, target_arch: simx64)
* gen_snapshot_x64 (universal binary composed of both of the above)

Note that host builds on macOS currently default to a host architecture of x64 (can be overridden via `--force-mac-arm64`) regardless of host architecture and thus, the build itself relies on Rosetta translation when invoked on Apple Silicon arm64 hardware. This is to ensure a consistent build in CI regardless of bot architecture. See: https://github.com/flutter/engine/blob/6fa734d686888a39add026a2a98d6ec311c23efb/tools/gn#L502-L505

Issue: flutter#101138
Issue: flutter#69157

Related issue: flutter#103386

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: auto-submit[bot]

build/archives/BUILD.gn

@@ -287,8 +287,8 @@ if (is_mac) {
     output = "$full_platform_name$suffix/gen_snapshot.zip"
     files = [
       {
-        source = "${root_out_dir}/gen_snapshot_${target_cpu}"
-        destination = "gen_snapshot_${target_cpu}"
+        source = "$root_out_dir/gen_snapshot_$target_cpu"
+        destination = "gen_snapshot_$target_cpu"
       },
     ]
   }

ci/licenses_golden/excluded_files

@@ -416,7 +416,6 @@
 ../../../flutter/sky/tools/create_embedder_framework.py
 ../../../flutter/sky/tools/create_full_ios_framework.py
 ../../../flutter/sky/tools/create_ios_framework.py
-../../../flutter/sky/tools/create_macos_binary.py
 ../../../flutter/sky/tools/create_macos_framework.py
 ../../../flutter/sky/tools/create_macos_gen_snapshots.py
 ../../../flutter/sky/tools/create_xcframework.py

lib/snapshot/BUILD.gn

@@ -186,54 +186,16 @@ if (host_os == "mac" && target_os != "mac" &&
 #
 # This target is used for builds targeting macOS.
 if (host_os == "mac" && target_os == "mac") {
-  template("build_mac_gen_snapshot") {
-    assert(defined(invoker.host_arch))
-    host_cpu = invoker.host_arch
-
-    build_toolchain = "//build/toolchain/mac:clang_$host_cpu"
-    if (host_cpu == target_cpu) {
-      gen_snapshot_target_name = "gen_snapshot_host_targeting_host"
-    } else {
-      gen_snapshot_target_name = "gen_snapshot"
-    }
-    gen_snapshot_target =
-        "$dart_src/runtime/bin:$gen_snapshot_target_name($build_toolchain)"
-
-    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")
-
-      sources = [ "${output_dir}/${gen_snapshot_target_name}" ]
-      outputs =
-          [ "${root_out_dir}/artifacts_$host_cpu/gen_snapshot_${target_cpu}" ]
-      deps = [ gen_snapshot_target ]
-    }
-  }
-
-  build_mac_gen_snapshot("create_macos_gen_snapshot_arm64_${target_cpu}") {
-    host_arch = "arm64"
-  }
-
-  build_mac_gen_snapshot("create_macos_gen_snapshot_x64_${target_cpu}") {
-    host_arch = "x64"
-  }
+  copy("create_macos_gen_snapshots") {
+    # The toolchain-specific output directory. For cross-compiles, this is a
+    # clang-x64 or clang-arm64 subdirectory of the top-level build directory.
+    host_output_dir =
+        get_label_info("$dart_src/runtime/bin:gen_snapshot($host_toolchain)",
+                       "root_out_dir")
 
-  action("create_macos_gen_snapshots") {
-    script = "//flutter/sky/tools/create_macos_binary.py"
+    sources = [ "${host_output_dir}/gen_snapshot" ]
     outputs = [ "${root_out_dir}/gen_snapshot_${target_cpu}" ]
-    args = [
-      "--in-arm64",
-      rebase_path("${root_out_dir}/artifacts_arm64/gen_snapshot_${target_cpu}"),
-      "--in-x64",
-      rebase_path("${root_out_dir}/artifacts_x64/gen_snapshot_${target_cpu}"),
-      "--out",
-      rebase_path("${root_out_dir}/gen_snapshot_${target_cpu}"),
-    ]
-    deps = [
-      ":create_macos_gen_snapshot_arm64_${target_cpu}",
-      ":create_macos_gen_snapshot_x64_${target_cpu}",
-    ]
+    deps = [ "$dart_src/runtime/bin:gen_snapshot($host_toolchain)" ]
   }
 }