feat(pg): allow creating indexes on 3+ columns mixing columns and expressions

[lbguilherme]

Previously this would fail:

export const TestTable = pgTable(
  'TestTable',
  {
    id: uuid('id').defaultRandom().primaryKey().notNull(),
    foo: text('foo'),
    bar: text('bar'),
    json: jsonb('json'),
  },
  table => {
    return {
      idx: index('idx').using(
        'btree',
        table.foo,
        sql`(${table.json}->>'id')`,
        table.bar, // error!
      ),
    };
  },
);

Starting from the second argument, every index expression must be a column or all of them must be SQL expressions, they can't mix. This is a typing error.

As a workaround, it is possible to do this:

      idx: index('idx').using(
        'btree',
        table.foo,
        sql`(${table.json}->>'id')`,
        sql`${table.bar}`, // redundant, but ok
      ),

This patch fixes the typing.