Write a specification for the `definition.json` files found in our open source PDKs

[mithro]

We should have a specification for the definition.json file found in our open source PDKs.

There is some details in https://bit.ly/open-source-pdks-naming

Example files;

• https://github.com/google/skywater-pdk-libs-sky130_fd_sc_hd/blob/main/cells/a2111o/definition.json
• https://github.com/google/skywater-pdk-libs-sky130_fd_sc_hd/blob/main/cells/sdfrtn/definition.json

We should also have a JSON schema for the format.

[mithro]

FYI - @proppy / @atorkmabrains

[mithro]

Example of a pull request adding these -> google/globalfoundries-pdk-libs-gf180mcu_fd_sc_mcu9t5v0#8

[proppy]

We should also have a JSON schema for the format.

+1, there are also support for describing using https://pydantic-docs.helpmanual.io/ which could give us typing in the scripts that process them (/cc @joamatab who was looking a something similar for @gdsfactory).