proto2lef: convert VLSIR layout proto to LEF description

[growly]

PTAL

This does not currently work. I use this input GDS and tech proto: inputs.zip.

The generated LEF is empty:

$ cat /tmp/test.lef
UNITS 
    DATABASE MICRONS 1000 ; 
END UNITS 
END LIBRARY 

[growly]

now that I populate the abstract field in the VLSIR cell per your slack suggestion, I get the error Invalid un-named layer for LEF export from layout21raw/src/lef.rs:128.

fresh inputs attached:
artefacts.zip

[growly]

Actually importing layer names from the proto fixes that problem. Once this has a test it's good to go.

[dan-fritchman]

Once this has a test it's good to go.

@growly, you adding that?