Fixes 4932 postgresql default constraint functions (#4934)

* Support functions in default column definition

e.g

CREATE TABLE t1 (

  c1 UUID DEFAULT gen_random_uuid(),

  c2 INTEGER DEFAULT nextval('some_seq')

);

* Add simple fixture test

dialects/postgresql/src/main/kotlin/app/cash/sqldelight/dialects/postgresql/grammar/PostgreSql.bnf

@@ -121,6 +121,7 @@ default_constraint ::= [ NOT NULL | NULL ] DEFAULT (
   current_timestamp_with_optional_interval |
   {signed_number} |
   {literal_value} |
+  {function_expr} |
   LP <<expr '-1'>> RP
 ) {
   extends = "com.alecstrong.sql.psi.core.psi.impl.SqlDefaultConstraintImpl"

dialects/postgresql/src/testFixtures/resources/fixtures_postgresql/column_types/Sample.s

@@ -70,7 +70,11 @@ CREATE TABLE all_types(
 
   some_interval_d TIMESTAMP NOT NULL DEFAULT NOW() - INTERVAL '5 days',
 
-  some_interval_e INTERVAL DEFAULT INTERVAL '3h' + INTERVAL '20m'
+  some_interval_e INTERVAL DEFAULT INTERVAL '3h' + INTERVAL '20m',
+
+  some_default_uuid UUID DEFAULT gen_random_uuid(),
+
+  some_default_sequence INTEGER DEFAULT nextval('some_seq')
 
 );