This PR #27515 change the logic if Table's `isPartitioned()` method.
But this method has 2 usages:
1. To check whether a table is range or list partitioned, for some DML operation such as Alter, Export.
For this case, it should return true if the table is range or list partitioned. even if it has only
one partition and one buckets.
2. To check whether the data is distributed (either by partitions or by buckets), for query planner.
For this case, it should return true if table has more than one bucket. Even if this table is not
range or list partitioned, if it has more than one bucket, it should return true.
So we should separate this method into 2, for different usages.
Otherwise, it may cause some unreasonable plan shape
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