sql/catalog/tabledesc: permit zero-valued column IDs in DependedOnBy

In 21.1 there was a bug whereby we would store a 0-value column ID in the
sequence's DependedOnBy because we'd add the depedency before allocating
an ID to the column. This bug was fixed in 21.2. Below is a reproduction
I've used to play with this bug:

```bash
roachprod wipe local
roachprod stage local release v21.1.3
roachprod run local -- mv cockroach cockroach-v21.1.3
roachprod stage local release v21.2.10
roachprod run local -- mv cockroach cockroach-v21.2.10
roachprod stage local release v22.1.1
roachprod run local -- mv cockroach cockroach-v22.1.1
roachprod start local --binary cockroach-v21.1.3
roachprod sql local -- -e "create table t1( i int primary key);
                           create table t2(i int primary key);
                           create sequence s1;
                           create sequence s2;
                           ALTER TABLE t1 ADD c1 BIGINT DEFAULT nextval('s1') NOT NULL;
                           ALTER TABLE t1 ADD c2 BIGINT DEFAULT nextval('s2') NOT NULL;
                           ALTER TABLE t2 ADD c1 BIGINT DEFAULT nextval('s1') NOT NULL;"
roachprod stop local
roachprod start local --binary cockroach-v21.2.10
while ! { roachprod sql local -- -e 'show cluster setting version' | grep 21.2 ; }; do sleep 1; done

roachprod sql local -- -e "alter table t1 add column c3 int default nextval('s1');
                           create table t3 (i int primary key);
                           alter table t3 add column c1 int default nextval('s1');"

roachprod stop local
roachprod start local --binary cockroach-v22.1.1
while ! { roachprod sql local -- -e 'show cluster setting version' | grep 22.1 ; }; do sleep 1; done
```

For now, for the rest of 22.1 we'll let this slide. As follow-up work, we'll
perform a migration to repair this situation and add back this validation once
the migration has been performed.

Release note (bug fix): In earlier 22.1 releases of cockroach, added validation
could cause problems for descriptors which carried invalid backreferences due
to an earlier bug in 21.1. This stricter validation could result in a variety
of query failures. This patch weakens the validation to permit the corruption
as we know it. A subsequent patch in 22.2 will be created to repair the invalid
reference.

pkg/sql/catalog/tabledesc/validate.go

@@ -306,6 +306,13 @@ func (desc *wrapper) validateInboundTableRef(
 		// descriptor is for a sequence. In this case, they refer to the columns
 		// in the referenced descriptor instead.
 		for _, colID := range by.ColumnIDs {
+			// Skip this check if the column ID is zero. This can happen due to
+			// bugs in 20.2.
+			//
+			// TODO(ajwerner): Make sure that a migration in 22.2 fixes this issue.
+			if colID == 0 {
+				continue
+			}
 			col, _ := backReferencedTable.FindColumnWithID(colID)
 			if col == nil {
 				return errors.AssertionFailedf("depended-on-by relation %q (%d) does not have a column with ID %d",

pkg/sql/catalog/tabledesc/validate_test.go

@@ -2491,6 +2491,40 @@ func TestValidateCrossTableReferences(t *testing.T) {
 				},
 			}},
 		},
+		{ // 14
+			// This case deals with a bug in version 21.1 and prior when
+			// ALTER TABLE ... ADD COLUMN ... DEFAULT nextval(...) would set the
+			// backreference ID to be 0 because it set up the backreference before
+			// calling AllocateIDs.
+			desc: descpb.TableDescriptor{
+				Name:                    "foo",
+				ID:                      51,
+				ParentID:                1,
+				UnexposedParentSchemaID: keys.PublicSchemaID,
+				SequenceOpts: &descpb.TableDescriptor_SequenceOpts{
+					Increment: 1,
+				},
+				DependedOnBy: []descpb.TableDescriptor_Reference{
+					{ID: 52, ColumnIDs: []descpb.ColumnID{0}},
+				},
+			},
+			otherDescs: []descpb.TableDescriptor{{
+				Name:                    "bar",
+				ID:                      52,
+				ParentID:                1,
+				UnexposedParentSchemaID: keys.PublicSchemaID,
+				PrimaryIndex: descpb.IndexDescriptor{
+					ID:             1,
+					Name:           "primary",
+					KeyColumnIDs:   []descpb.ColumnID{1},
+					KeyColumnNames: []string{"a"},
+				},
+				Columns: []descpb.ColumnDescriptor{
+					{Name: "a", ID: 1, Type: types.Int},
+				},
+				DependsOn: []descpb.ID{51},
+			}},
+		},
 	}
 
 	for i, test := range tests {