catalog/rewrite: rewrite declarative schema changer state for functions

The declarative schema changer state rewrite logic previously skipped
function descriptors. This was an oversight stemming from the fact that
function creation was limited to a single stage. However, with
schema_locked support, function creation involving table references can
now span multiple stages. This patch corrects the oversight by enabling
schema changer state rewriting for functions.

Release note: None

Author: fqazi

pkg/sql/catalog/rewrite/rewrite.go

@@ -892,6 +892,20 @@ func rewriteSchemaChangerState(
 					removeElementAtCurrentIdx()
 					continue
 				}
+			case *scpb.TriggerFunctionCall:
+				// If there is a missing function, then this was in middle of creating
+				// a trigger when the back-up was taken.
+				if el.FuncID == missingID {
+					removeElementAtCurrentIdx()
+					continue
+				}
+			case *scpb.TriggerDeps:
+				// If there is a missing function, then this was in middle of creating
+				// a trigger when the back-up was taken.
+				if catalog.MakeDescriptorIDSet(el.UsesRoutineIDs...).Contains(missingID) {
+					removeElementAtCurrentIdx()
+					continue
+				}
 			}
 			return errors.Wrap(err, "rewriting descriptor ids")
 		}
@@ -1176,6 +1190,9 @@ func FunctionDescs(
 					fnDesc.Name, dep.ID)
 			}
 		}
+		if err := rewriteSchemaChangerState(fnDesc, descriptorRewrites); err != nil {
+			return err
+		}
 	}
 	return nil
 }