feat: Add Google Cloud Spanner database support across Flowable engines

[Vaibhavch9876]

Summary

This PR introduces native support for Google Cloud Spanner using the GoogleSQL dialect across the Flowable engine suite.

Key Changes

1. Cloud Spanner JDBC Driver & Profile:
   • Introduced com.google.cloud:google-cloud-spanner-jdbc:2.27.0 in flowable-dependencies.
   • Added -Pspanner profile in flowable-parent.
2. Dialect & Database Type Resolution:
   • Added DATABASE_TYPE_SPANNER = "spanner" in DbUtil and AbstractEngineConfiguration.
   • Added Spanner SQL properties (spanner.properties) and configured NULLS FIRST / NULLS LAST order-by formatting in ListQueryParameterObject.
   • Configured Spanner schema metadata filtering in TableDataManagerImpl and AbstractSqlScriptBasedDbSchemaManager.
3. Transaction Abort Retries & Primary Keys:
   • Implemented SpannerRetryInterceptor for transparent exponential backoff on Spanner transaction aborts (gRPC code 10 ABORTED).
   • Defaulted entity ID generator on Spanner to StrongUuidGenerator to prevent root-split write hotspotting (GSQL-C1).
4. GoogleSQL MyBatis Mapper Compatibility:
   • Adjusted 11 bulk delete MyBatis XML mappers (HistoricDetail, HistoricActivityInstance, HistoricVariableInstance, HistoricTaskLogEntry, etc.) to omit aliases between DELETE and FROM.
5. GoogleSQL DDL Scripts:
   • Authored complete GoogleSQL schema creation and teardown scripts for Common, Process Engine, History, IDM, CMMN, DMN, App, Event Registry, and the unified distribution script (distro/sql/create/all/flowable.spanner.all.create.sql).
   • Structured drop scripts in strict reverse dependency order: Foreign Keys -> Secondary Indexes -> Tables.
6. Testing & CI Harness:
   • Added flowable.spanner.cfg.xml and SpannerEngineIntegrationTest in flowable-engine.
   • Added GitHub Actions workflow .github/workflows/spanner.yml running against Cloud Spanner Emulator.

Compatibility

• Preserves 100% backward compatibility with existing databases (H2, MySQL, PostgreSQL, Oracle, DB2, etc.).
• Default build and test execution remain untouched.