implement spreads in GQ(q,q)

[dimpase]

in #30223 Ivo implemented spreads in GQ(q,q²), but we should also have spreads in GQ(q,q), to get more drgs as in #30337

Alerted on this possibility by Krystal Guo in https://twitter.com/guo_krystal/status/1377295829669662726

Replying to 
@guo_krystal
Having painstakingly entered it into @sagemath
I discovered that it was a graph I knew!
It is GQ(2,2) with a spread deleted.
So it is an antipodal distance regular graph on 15 vertices with {4,2,1;1,1,4}. 3/n
5:24 PM · Mar 31, 2021

CC: @Ivo-Maffei

Component: graph theory

Issue created by migration from https://trac.sagemath.org/ticket/31587