Add OID descriptions to dumped parse/query/plan trees

Hi Hackers,

When reading dumped parse/query/plan trees, sometime we want to know what exact type/operator/function an OID stands for. I just added a new feature that will add some OID descriptions to the dump trees, like:

```

      :scan.scanrelid 1
      :indexid 16474 # index orders_pkey
      :indexqual (
         {OPEXPR
         :opno 521 # operator >(integer,integer)
         :opfuncid 147 # function int4gt(integer,integer)
         :opresulttype 16 # type boolean
         :opretset false
         :opcollid 0

```

The patch file is attached.

Best regards,

--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/