support subscript for hstore

support subscript for hstore

Added support for PostgreSQL 14+ HSTORE subscripting syntax. When connected
to PostgreSQL 14 or later, HSTORE columns now automatically use the native
subscript notation ``hstore_col['key']`` instead of the arrow operator
``hstore_col -> 'key'`` for both read and write operations. This provides
better compatibility with PostgreSQL's native HSTORE subscripting feature
while maintaining backward compatibility with older PostgreSQL versions.

as part of this change we add a new parameter to custom_op "visit_name"
which allows a custom op to refer to a specific visit method in a
dialect's compiler.

Fixes: #12948
Change-Id: Id98d333fe78e31d9c7679cb2902f1c7e458d6e11