feat(format): add constraint_expression to GetObjects

Closes #3987.

Author: lidavidm

c/include/arrow-adbc/adbc.h

@@ -1766,11 +1766,16 @@ AdbcStatusCode AdbcConnectionGetInfo(struct AdbcConnection* connection,
 /// | constraint_type          | utf8 not null           | (1)      |
 /// | constraint_column_names  | list<utf8> not null     | (2)      |
 /// | constraint_column_usage  | list<USAGE_SCHEMA>      | (3)      |
+/// | constraint_expression    | utf8                    | (4)      |
 ///
-/// 1. One of 'CHECK', 'FOREIGN KEY', 'PRIMARY KEY', or 'UNIQUE'.
+/// 1. One of 'CHECK', 'FOREIGN KEY', 'PRIMARY KEY', or 'UNIQUE', or a
+///    vendor-specific type.
 /// 2. The columns on the current table that are constrained, in
 ///    order.
 /// 3. For FOREIGN KEY only, the referenced table and columns.
+/// 4. [Since version 1.2.0] If supported, the vendor-specific definition of
+///    the constraint (e.g. the SQL expression to be checked).  This field is
+///    optional.
 ///
 /// USAGE_SCHEMA is a Struct with fields:
 ///
@@ -1781,6 +1786,12 @@ AdbcStatusCode AdbcConnectionGetInfo(struct AdbcConnection* connection,
 /// | fk_table                 | utf8 not null           |
 /// | fk_column_name           | utf8 not null           |
 ///
+/// Starting in version 1.2.0, optional fields were introduced to the schema.
+/// Optional fields may not be present and applications should check before
+/// using them.  Drivers may choose to include optional fields (with null
+/// values).  If an optional field is present, all optional fields defined
+/// before it in the schema must be present.
+///
 /// This AdbcConnection must outlive the returned ArrowArrayStream.
 ///
 /// \param[in] connection The database connection.