Adding back handleLArCustom() to GeoShapeAction.

This is needed to fix the Athena master build. When removing the LArCustomShape from GeoModelIO, in fact, all occurrences of LArCustomShape were removed from GeoModelKernel as well; but Athena still uses them, in particular the handleLArCustom() method of the GeoShapeAction class.

For details:

• athena!31618 (comment 3321141)
• GeoModelDev/GeoModelCore@62142525

Pinging @akraszna , @boudreau , @tsulaia , @mbandier , @dellacqu

I'm sorry, but no. Ric, please check the discussions before doing this much work.

closed

mentioned in merge request athena!31618 (merged)

Thanks, Attila for your changes.

AE Build SUCCESS
Build logfiles are available at Jenkins [AE-MERGE-REQUEST-CC7 #229]