klayout density check specific to sky130 tech

[kassemmkk]

Originally created by proppy on 2022-11-10T22:27:20Z

https://github.com/efabless/mpw_precheck/blob/main/checks/drc_checks/klayout/met_min_ca_density.lydrc

found some density tests the klayout drc
deck for g180mcu:
https://github.com/google/globalfoundries-pdk-libs-gf180mcu_fd_pr/blob/92ec4b2e5eb193a0c5c2754413d44981c8e17e16/rules/klayout/drc/gf180mcu_density.drc

Is there more needed here?

Part of #146