Some LEF/DEF to GDS layer mappings are missing

[antonblanchard]

I was trying to understand why DEF files in klayout had issues naming layers. In KLayout/klayout#700 the klayout maintainer points out that we are missing some LEF/DEF to GDS layer mappings.

There isn't a mapping for "met4" for example. In fact all the metal layers and via layers need a mapping.