feat: populate `.repo-metadata.json` from highest version

[JoeWang1127]

In this PR:

• populate .repo-metadata.json from highest stable version of proto paths.

The .repo-metadata.json is only generated once per library and the first item in proto paths is used, so the proto paths with the highest stable version should be the first item after sorting the proto paths in the library.

The method used to compare two proto paths, a and b:

1. if both of a and b don't have a version, the one with lower depth is smaller.
2. if either a or b has a version, the one with the version is smaller.
3. if either a or b has a stable version, but not both, the one with the stable version is smaller, e.g., google/spanner/v2 is smaller than google/spanner/v3beta.
4. if both a and b have a non-stable version, the one with higher version is smaller, e.g., google/spanner/v2beta1 is smaller than google/spanner/v2alpha2.
5. if both a and b have a stable version, the one with lower depth is smaller, e.g., google/spanner/v1 is smaller than google/spanner/admin/v1, google/spanner/v1 is smaller than google/spanner/admin/v2
6. if both a and b have a stable version and the depth is the same, the one with higher version is smaller, e.g., google/spanner/v2 is smaller than google/spanner/v1.

Test the change:

1. build the image locally:

   docker build -f .cloudbuild/library_generation/library_generation.Dockerfile -t local:latest .

2. build the generator locally:

   mvn -V -B -ntp clean install -DskipTests

3. run the image:

   docker run --rm -u "$(id -u):$(id -g)" -v "$(pwd):/workspace" -v "$HOME/.m2:/home/.m2" local:latest

Result:

1. no change in common protos
2. transport changed to both in java-iam/.repo-metadata.json. This is expected since the transport in google/iam/v2/BUILD.bazel is grpc+rest. Without this change, the transport is parsed from google/iam/v2/BUILD.bazel, which doesn't have a java_gapic_library target, thus the value is grpc by default.

[sonarcloud[bot]]

Quality Gate passed for 'gapic-generator-java-root'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[sonarcloud[bot]]

Quality Gate passed for 'java_showcase_integration_tests'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[JoeWang1127]

QQ, Don't we have .repo-metadata golden files for our units? Maybe we can change one of these to test the proto_path sorting criteria

The golden files are used in testing .repo-metadata.json generation, generate_prerequisite_files to be specific.

If we want to test generating this file with a library_config (from which contains multiple proto_path), we need test generate_composed_library, which is not easy to do since this function aggregates many "small" functions and is tested in integration test.