Implement Meta.equals() and hashCode() based on Meta.ddl()

[lukaseder]

In addition to the debugging utility introduced with #9428, we should also allow for comparing two Meta implementations based on their produced ddl()

If two Meta instances are equal, then their diff is empty:

Meta m1 = ...
Meta m2 = ...

if (m1.equals(m2)) {
  assertEquals(0, m1.diff(m2))
  assertEquals(0, m2.diff(m1))
}

Unlike in the debugging utility #9428, we're not adding any performance considerations here. If users want to compare equality, then they will be willing to pay the price if the specific Meta implementation originates from a JDBC DatabaseMetaData set of queries.

[lukaseder]

There's some subtlety to think about here. Are these two tables equal?

create table t (a int, b int);
create table t (b int, a int);

They could be seen equal or not. Both options are possible. Also, are these two databases equal?

-- DB1
create schema s1;
create schema s2;

-- DB2
create schema s2;
create schema s1;

In the latter case, we could argue that Meta.ddl() should produce schemas in a predictable order.

We can fix both of these things via: #9434

[lukaseder]

We won't reorder the columns but use the new defaults for #9434. This fixes the schema order but not the column order.