Implement REPO.bazel

- REPO.bazel is a new file at the root of repos that can only contain a `repo()` call with a bunch of package default arguments (similar to `package()`)
- A new SkyFunction, RepoFileFunction, evaluates a REPO.bazel file and returns the `PackageArgs` object containing those arguments
- PackageFunction for packages in repo `@foo` now depends on RepoFileFunction for `@foo`

Fixes bazelbuild/bazel#18077

PiperOrigin-RevId: 551313372

third_party/bazel/src/main/protobuf/failure_details.proto

@@ -1243,6 +1243,7 @@ message PackageLoading {
     BUILTINS_INJECTION_FAILURE = 29 [(metadata) = { exit_code: 1 }];
     SYMLINK_CYCLE_OR_INFINITE_EXPANSION = 30 [(metadata) = { exit_code: 1 }];
     OTHER_IO_EXCEPTION = 31 [(metadata) = { exit_code: 36 }];
+    BAD_REPO_FILE = 32 [(metadata) = { exit_code: 1 }];
   }
 
   Code code = 1;