Fix: added some null pointer dereference checks

[wavyfuncollaps]

These changes harden the GradleBuildServerBuildSupport class against four null-dereference scenarios:

• Skip project dependencies that do not map to an Eclipse workspace project.
• Reject non-file output URIs when conversion produces no filesystem path.
• Skip JVM build targets with missing or invalid decoded metadata.
• Skip Maven dependencies with missing or invalid decoded metadata.
  Each case writes a meaningful log message containing relevant identifiers before safely continuing or returning.

[wenyt (wenytang-ms)]

wavyfuncollaps thank you for your contribution, can you add some test cases for this pr?