Feat!: transpile map retrieval to duckdb, transpile TRY_ELEMENT_AT

[georgesittas]

DuckDB says the following for retrieving values from maps:

MAPs use bracket notation for retrieving values. Selecting from a MAP returns a LIST rather than an individual value, with an empty LIST meaning that the key was not found.

This makes it tricky to transpile such retrievals to / from it, because we need to either unwrap / wrap the retrieved value, respectively.

This PR:

• implements a best-effort approach to handle the -> DuckDB direction of the transpilation
• facilitates the transpilation of Spark's TRY_ELEMENT_AT function

One side effect of this change is that when constructing Bracket nodes for DuckDB manually, it will also be required to set returns_list_for_maps to True, otherwise we'll generate incorrect SQL when targeting DuckDB.

References:

• https://spark.apache.org/docs/latest/api/sql/index.html#try_element_at
• https://docs.databricks.com/en/sql/language-manual/functions/try_element_at.html
• https://duckdb.org/docs/sql/data_types/map#retrieving-from-maps
• https://duckdb.org/docs/sql/data_types/array.html