Write Liberty Files (+ Support liberty for synthesizing designs with macros?)

[donn]

Prompt

OpenROAD has had an experimental feature to write_liberty for a while. The values reportedly aren't that accurate but we feel like generating a basic lib file for things like synthesis has its merit.

On that note, OpenLane doesn't officially support liberty files for synthesizing designs with macros- requiring black-boxed Verilog models instead.

Proposal

Add liberty writing (requires #1244 to be merged)