sql: add support for row-level AFTER triggers

[DrewKimball]

This issue tracks adding support for row-level AFTER triggers, which execute for each mutated row in an INSERT, UPDATE, UPSERT, or DELETE after the mutation occurs, as well as any checks and cascades. Example:

CREATE TRIGGER t AFTER UPDATE ON table_1 FOR EACH ROW EXECUTE FUNCTION f();

Jira issue: CRDB-37296

Jira issue: CRDB-39861