geo/geomfn: implement ST_SymmetricDifference

Added ST_SymmetricDifference builtin.

ST_SymmetricDifference is simply an alias for ST_SymDifference.

Release justification: low-risk update to new functionality
Release note (sql change): Implemented the geometry based builtin
`ST_SymmetricDifference`.

Resolves: cockroachdb#49052

docs/generated/sql/functions.md

@@ -1641,6 +1641,9 @@ The paths themselves are given in the direction of the first geometry.</p>
 <tr><td><a name="st_symdifference"></a><code>st_symdifference(geometry_a: geometry, geometry_b: geometry) &rarr; geometry</code></td><td><span class="funcdesc"><p>Returns the symmetric difference of both geometries.</p>
 <p>This function utilizes the GEOS module.</p>
 </span></td></tr>
+<tr><td><a name="st_symmetricdifference"></a><code>st_symmetricdifference(geometry_a: geometry, geometry_b: geometry) &rarr; geometry</code></td><td><span class="funcdesc"><p>Returns the symmetric difference of both geometries.</p>
+<p>This function utilizes the GEOS module.</p>
+</span></td></tr>
 <tr><td><a name="st_touches"></a><code>st_touches(geometry_a: geometry, geometry_b: geometry) &rarr; <a href="bool.html">bool</a></code></td><td><span class="funcdesc"><p>Returns true if the only points in common between geometry_a and geometry_b are on the boundary. Note points do not touch other points.</p>
 <p>This function utilizes the GEOS module.</p>
 <p>This function variant will attempt to utilize any available geospatial index.</p>