feat(gds): use .oas from user projects when available

Author: htfab

.github/workflows/gds.yaml

@@ -85,7 +85,13 @@ jobs:
               brotli -jd $project/$project.gds.br
             fi
             
-            python ../sky130_density_fix/replace_decap.py --design $project --user-gds $project/$project.gds --replacement-gds ../sky130_density_fix/sky130_ef_sc_hd__newfill_12.gds | tee -a ../tt-multiplexer/ol2/tt_top/gds/replace_decap.log
+            if [ -f $project/$project.gds ]; then
+              python ../sky130_density_fix/replace_decap.py --design $project --user-gds $project/$project.gds --replacement-gds ../sky130_density_fix/sky130_ef_sc_hd__newfill_12.gds | tee -a ../tt-multiplexer/ol2/tt_top/gds/replace_decap.log
+            fi
+
+            if [ -f $project/$project.oas ]; then
+              python ../sky130_density_fix/replace_decap.py --design $project --user-gds $project/$project.oas --replacement-gds ../sky130_density_fix/sky130_ef_sc_hd__newfill_12.gds | tee -a ../tt-multiplexer/ol2/tt_top/gds/replace_decap.log
+            fi
           done
 
       # run OpenLane to build the GDS