[SPARK-3800][SQL] Clean aliases from grouping expressions

Author: Michael Armbrust <michael@databricks.com>

Closes #2658 from marmbrus/nestedAggs and squashes the following commits:

862b763 [Michael Armbrust] Merge remote-tracking branch 'origin/master' into nestedAggs
3234521 [Michael Armbrust] Merge remote-tracking branch 'origin/master' into nestedAggs
8b06fdc [Michael Armbrust] possible fix for grouping on nested fields