Optimize _ST_OrderingEquals by using gserialized_cmp

[Algunenano]

Same idea as ​https://trac.osgeo.org/postgis/ticket/4453 but for ST_OrderingEquals since we already have gserialized_cmp to do this.

Query: I'm avoiding ST_OrderingEquals and using _ST_OrderingEquals on purpose to check the impact on that change alone:

Select * from all_month INNER JOIN all_month b ON _ST_OrderingEquals(all_month.the_geom, b.the_geom);

Before:

Time: 27684.750 ms (00:27.685)

After:

Time: 13964.775 ms (00:13.965)

GH PR: ​https://github.com/postgis/postgis/pull/444

[Raul Marin]

In 17601:

_ST_OrderingEquals: Avoid deserialization

Closes #4454
Closes ​https://github.com/postgis/postgis/pull/444