Set output_files on the toolchain

This avoids having to use the deprecated argument to `proto_common.compile`.

PiperOrigin-RevId: 547475903

Author: thomasvl

swift/internal/BUILD

@@ -13,6 +13,7 @@ proto_lang_toolchain(
     name = "proto_swift_toolchain",
     command_line = "--swift_out=$(OUT)",
     mnemonic = "ProtocGenSwift",
+    output_files = "multiple",
     plugin = "@com_github_apple_swift_protobuf//:ProtoCompilerPlugin",
     plugin_format_flag = "--plugin=protoc-gen-swift=%s",
     progress_message = "Generating Swift sources for %{label}",

swift/internal/swift_protoc_gen_aspect.bzl

@@ -231,8 +231,6 @@ def _swift_protoc_gen_aspect_impl(target, aspect_ctx):
             additional_inputs = depset(direct = [transitive_module_mapping_file]),
             experimental_exec_group = _GENERATE_EXEC_GROUP,
             generated_files = pbswift_files,
-            # ??? Docs says this is deprecated, but seems to be required
-            plugin_output = aspect_ctx.bin_dir.path,
             proto_info = target_proto_info,
             proto_lang_toolchain_info = proto_lang_toolchain_info,
         )