Feat(duckdb): add support for simplified pivot syntax

[georgesittas]

Fixes #1712

Also added support for the standalone FROM tbl expression (see example below) which is used in DuckDB's pivot examples. This is essentially a shorthand for SELECT * FROM tbl and it seems useful to support in the base parser. We could also improve the from_ helper to allow from_(..., star=True) as a way to dry up exp.select("*").from_(...). @tobymao thoughts on this?

>>> import duckdb
>>> duckdb.connect().execute("with t as (select 1) select * from (from t)").fetchdf()
   1
0  1
>>> duckdb.connect().execute("with t as (select 1) from (from t)").fetchdf()
   1
0  1

References:

• https://duckdb.org/docs/sql/statements/pivot
• https://duckdb.org/docs/sql/query_syntax/from#examples