Implements #8952

This PR implements support for qualified identifiers in the EXCLUDE clause, i.e.:

SELECT * EXCLUDE (tbl.col) FROM tbl;

Fully qualified identifiers are supported (i.e. db.schema.tbl.col). Any non-provided identifiers are considered as "matching all", i.e. i matches all columns named i, tbl.i matches all columns named i within tables named tbl, etc.

In order to preserve backwards compatibility, unqualified identifiers are serialized using the old case_insensitive_set. Only qualified identifiers are serialized using the qualified_column_set.