Enforce V8 artifact profiles at Bazel target boundaries (#57165)

## Why

V8 source and release artifacts require different ABI and C++ runtime settings. Selecting a named artifact should also select its required settings, without callers coordinating separate sandbox, pointer compression, libc++, and CPU flags.

## What changed

- Add Bazel transitions for `source`, `release`, and `sandbox_release` profiles. Source builds use the sandbox ABI and workspace runtime; release pairs use Chromium's pinned runtime with their respective ABI.
- Select the V8 CPU from the artifact target and enforce matching target platform constraints.
- Make the underlying V8 settings unavailable as CLI flags and remove redundant configuration from release tooling and workflows.
- Select Darwin/Linux prebuilts solely through `rusty_v8_from_source`, keeping source archives and bindings paired when enabled.

GitOrigin-RevId: f72fc06b6f74b79ab2ab8ca697e4f2006076a833

.github/scripts/test_rusty_v8_bazel.py

@@ -25,7 +25,7 @@ class RustyV8BazelTest(unittest.TestCase):
             "aarch64_pc_windows_gnullvm",
             "aarch64_pc_windows_msvc",
             "aarch64_unknown_linux_gnu_bazel",
-            "aarch64_unknown_linux_musl_release_base",
+            "aarch64_unknown_linux_musl_release",
             "x86_64_apple_darwin_bazel",
             "x86_64_pc_windows_gnullvm",
             "x86_64_pc_windows_msvc",
@@ -72,22 +72,6 @@ class RustyV8BazelTest(unittest.TestCase):
             with patch.object(rusty_v8_bazel, "MODULE_BAZEL", module_bazel):
                 self.assertEqual("146.4.0", rusty_v8_bazel.command_version(None))
 
-    def test_artifact_bazel_configs_always_enable_upstream_libcxx(self) -> None:
-        self.assertEqual(
-            ["rusty-v8-upstream-libcxx"],
-            rusty_v8_bazel.artifact_bazel_configs(),
-        )
-        self.assertEqual(
-            ["rusty-v8-upstream-libcxx", "v8-release-compat"],
-            rusty_v8_bazel.artifact_bazel_configs(["v8-release-compat"]),
-        )
-        self.assertEqual(
-            ["rusty-v8-upstream-libcxx", "v8-release-compat"],
-            rusty_v8_bazel.artifact_bazel_configs(
-                ["rusty-v8-upstream-libcxx", "v8-release-compat"]
-            ),
-        )
-
     def test_bazel_commands_use_shared_buildbuddy_remote_config_library(self) -> None:
         with patch.dict(environ, {}, clear=True):
             self.assertEqual(
@@ -276,7 +260,7 @@ class RustyV8BazelTest(unittest.TestCase):
                         "macos_arm64",
                         ["//third_party/v8:pair"],
                         "opt",
-                        ["rusty-v8-upstream-libcxx"],
+                        ["ci-macos"],
                     ),
                 )
 
@@ -284,14 +268,14 @@ class RustyV8BazelTest(unittest.TestCase):
                 "macos_arm64",
                 ["//third_party/v8:pair"],
                 "opt",
-                ["rusty-v8-upstream-libcxx"],
+                ["ci-macos"],
                 download_toplevel=True,
             )
             bazel_output_files.assert_called_once_with(
                 "macos_arm64",
                 ["//third_party/v8:pair"],
                 "opt",
-                ["rusty-v8-upstream-libcxx"],
+                ["ci-macos"],
             )
 
     def test_update_module_bazel_replaces_and_inserts_sha256(self) -> None: