chore: import upstream snapshot with attribution

testing/generation/command_docs/synopses/create_trigger.txt

@@ -0,0 +1,32 @@
+CREATE [ OR REPLACE ] CONSTRAINT TRIGGER $name$ AFTER { $event$ [ OR ... ] }
+    ON $table_name$
+    FROM $referenced_table_name$
+    [ NOT DEFERRABLE | [ DEFERRABLE ] [ INITIALLY IMMEDIATE | INITIALLY DEFERRED ] ]
+    FOR EACH ROW
+    [ WHEN ( $condition$ ) ]
+    EXECUTE { FUNCTION | PROCEDURE } $function_name$ ( $arguments$ )
+
+CREATE [ OR REPLACE ] TRIGGER $name$ BEFORE { $event$ [ OR ... ] }
+    ON $table_name$
+    [ FOR [ EACH ] { ROW | STATEMENT } ]
+    [ WHEN ( $condition$ ) ]
+    EXECUTE { FUNCTION | PROCEDURE } $function_name$ ( $arguments$ )
+
+CREATE [ OR REPLACE ] TRIGGER $name$ AFTER { $event$ [ OR ... ] }
+    ON $table_name$
+    [ REFERENCING { { OLD | NEW } TABLE [ AS ] $transition_relation_name$ } [ ... ] ]
+    [ FOR [ EACH ] { ROW | STATEMENT } ]
+    [ WHEN ( $condition$ ) ]
+    EXECUTE { FUNCTION | PROCEDURE } $function_name$ ( $arguments$ )
+
+CREATE [ OR REPLACE ] TRIGGER $name$ INSTEAD OF { $event$ [ OR ... ] }
+    ON $table_name$
+    [ FOR [ EACH ] { ROW | STATEMENT } ]
+    EXECUTE { FUNCTION | PROCEDURE } $function_name$ ( $arguments$ )
+
+where $event$ is:
+
+INSERT |
+    UPDATE [ OF $column_name$ [ , ... ] ] |
+    DELETE |
+    TRUNCATE