chore(query-orchestrator): Extract Pre-aggregation-related classes to separate files #3712

Job	Run time
Build native Linux 20 x86_64-unknown-linux-gnu Python fallback	2m 54s
latest-tag-sha	24s
build	7m 15s
tests (20.x, athena-export-bucket-s3)	18m 54s
tests (20.x, bigquery-export-bucket-gcs)	8m 57s
tests (20.x, clickhouse)	5m 17s
tests (20.x, clickhouse-export-bucket-s3)	5m 59s
tests (20.x, databricks-jdbc)	6m 15s
tests (20.x, databricks-jdbc-export-bucket-s3)	6m 32s
tests (20.x, databricks-jdbc-export-bucket-azure)	6m 31s
tests (20.x, mssql)	5m 39s
tests (20.x, mysql)	5m 4s
tests (20.x, postgres)	5m 11s
tests (20.x, redshift)	5m 57s
tests (20.x, redshift-export-bucket-s3)	6m 0s
tests (20.x, snowflake)	6m 11s
tests (20.x, snowflake-export-bucket-s3)	5m 48s
tests (20.x, snowflake-export-bucket-azure)	5m 45s
tests (20.x, snowflake-export-bucket-azure-via-storage-integration)	5m 42s
tests (20.x, snowflake-export-bucket-gcs)	5m 55s
	2h 6m 10s

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