tests: Add java-showcase-3.21.0 (googleapis#4081)

Add a new module java-showcase-3.21.0. This is a copy of the
java-showcase module with a different version (3.21.0) of protobuf gen
code. This is intended to test the compatibility between protobuf
runtime v4.33.x and gen code 3.21.0.

The [gen code contains makeExtensionsImmutable
method](https://github.com/googleapis/sdk-platform-java/blob/c80004ad3fdafbf43aa9adf4e8069ac3b4fefaa4/java-showcase-3.21.0/proto-gapic-showcase-v1beta1/src/main/java/com/google/showcase/v1beta1/AttemptSequenceRequest.java#L90)
which proves that it is generated with a protoc version prior to 3.21.7.

Add [a new
step](https://github.com/googleapis/sdk-platform-java/blob/c80004ad3fdafbf43aa9adf4e8069ac3b4fefaa4/.github/workflows/ci.yaml#L313-L319)
in CI to test this module.

Author: blakeli0

.github/workflows/ci.yaml

@@ -303,6 +303,13 @@ jobs:
           mvn clean verify -P '!showcase,enable-integration-tests,loggingTestBase,disabledLogging'  \
             --batch-mode \
             --no-transfer-progress
+      - name: Showcase integration tests - Protobuf gen code 3.21.0
+        working-directory: java-showcase-3.21.0
+        run: |
+          mvn verify \
+            -P enable-integration-tests \
+            --batch-mode \
+            --no-transfer-progress
   showcase:
     runs-on: ubuntu-22.04
     strategy:
@@ -423,7 +430,7 @@ jobs:
       run: |
         mvn install -B -ntp -DskipTests -Dclirr.skip -Dcheckstyle.skip -Dfmt.skip
     - name: Validate gapic-generator-java-bom
-      uses: googleapis/java-cloud-bom/tests/validate-bom@ef3656d3c66f4c6bd3b2c569d64a77cb40aeb77e
+      uses: googleapis/java-cloud-bom/tests/validate-bom@47ad868794c5d38ee7eb95d69371a7a79f84d890
       with:
         bom-path: gapic-generator-java-bom/pom.xml
 

java-showcase-3.21.0/README.md

@@ -0,0 +1,2 @@
+This is a copy of [GAPIC Showcase](https://github.com/googleapis/gapic-showcase) with protobuf 3.21.0 gen code.
+This is intended to test the compatibility between protobuf-java runtime v4.33.0 and gen code 3.21.0.  

java-showcase-3.21.0/gapic-showcase-extended/proto/BUILD.bazel

@@ -0,0 +1,34 @@
+# Copyright 2023 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Provides proto_library target
+Exports grpc service config
+"""
+load ("@rules_proto//proto:defs.bzl", "proto_library")
+
+# This is an API workspace, having public visibility by default makes perfect sense.
+package(default_visibility = ["//visibility:public"])
+
+# This BUILD file is the framework for gapic-showcase-extended (an extension to the existing gapic-showcase)
+# It serves to augment the existing showcase project with generic protos not *yet* suited to the upstream project
+#
+# gapic-showcase project is used to test the generated client behavior with a showcase server
+# gapic-showcase-extension project is used to test the generator's behavior
+
+#proto_library(
+#  name = "showcase_proto_extended",
+#  srcs = [],
+#  deps = []
+#)

java-showcase-3.21.0/gapic-showcase-extended/proto/wicked.proto

@@ -0,0 +1,49 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+import "google/api/client.proto";
+
+package google.showcase.v1beta1;
+
+option go_package = "github.com/googleapis/gapic-showcase/server/genproto";
+option java_package = "com.google.showcase.v1beta1";
+option java_multiple_files = true;
+option ruby_package = "Google::Showcase::V1beta1";
+
+// This service is used to show a Service with either non-enabled or non-eligible
+// RPCs for HttpJson (Http 1.1).
+// Non-Enabled: Missing the (google.api.http) annotation to enabled it
+// Non-Eligible: BIDI and Client side streaming are not supported with Http 1.1
+// Service name is reference to `No REST for the Wicked`
+service Wicked {
+  // This service is meant to only run locally on the port 7469 (keypad digits
+  // for "show").
+  option (google.api.default_host) = "localhost:7469";
+
+  rpc CraftEvilPlan(EvilRequest) returns (EvilResponse);
+
+  rpc BrainstormEvilPlans(stream EvilRequest) returns (stream EvilResponse);
+
+  rpc PersuadeEvilPlan(stream EvilRequest) returns (EvilResponse);
+}
+
+message EvilRequest {
+  string malicious_idea = 1;
+}
+
+message EvilResponse {
+  string malicious_plan = 1;
+}