[FEATURE][Calcite Engine] Support access to nested fields after command `FIELDS`

[qianheng-aws]

Is your feature request related to a problem?
Need to support access nested fields after command FIELDS.

PPL like below, although it has projection only includes field city, we still expect to use nested field city.name since it's nested in field city.

source=sql_test_index__deep_nested | fields city | sort city.name

Background:
PPL will expand and flatten all nested fields in it's table schema, so we can access them easily.