WL#2388: GIS: Add synonym for GeometryCollection & NumInteriorRings

MySQL will implement a synonym for the GIS GeometryCollection 
type (GeomCollection) and also for the GIS NumInteriorRings
function (NumInteriorRing).

Rationale 
--------- 
Support for the GeomCollection type and the NumInterioRing
function is required so that MySQL can claim compliance 
with OpenGIS; see WL#2377 for full details.

Syntax
------

1) MySQL has implemented a GeometryCollection type, or class. 
The OpenGIS specification also calls this the GeomCollection 
type. For compatibility with the standard, MySQL must implement:
GeomCollection

-- GeomCollection is a synonym for GeometryCollection. No other 
changes need to be made.



2) MySQL has implemented a NumInteriorRings function, which takes 
one argument -- a polygon value -- and returns an integer 
representing the number of interior rings included in the polygon. 
NumInteriorRings is either a typo or taken from a too-early version 
of the OpenGIS specification, which always calls this the 
NumInteriorRing function. For compatibility with the standard, 
MySQL must implement:
NumInteriorRing(polygon_value)

-- NumInteriorRing is a synonym for NumInteriorRings. No other
changes need to be made.