pdn/odb: move global connection rules to ODB

[openroad-robot]

Adds:

• dbGlobalConnect class to ODB to hold the rules for global connections so they can be saved with the database.
• clear/report_global_connect helper functions to remove all rules and report defined rules.

Changes:

• PDN uses ODB to hold the values of the global connect rules.

This PR should allow for calling global_connect after the PDNGEN step (assuming the database was saved) and all the same rules are applied. This addresses: https://github.com/The-OpenROAD-Project/OpenROAD/issues/2157

[gadfort]

@maliberty I used the access points in ODB for this as a template. This will allow us to add a global_connect call at the very end of the flow to ensure all the power connection are made according to the rules defined.

[gadfort]

@maliberty I moved all the global connection code to ODB and remove it from PDN. I added the helper functions from PDN to dbBlock.

[maliberty]

It is best to avoid a force push on something that is already in review. I can't see the changes since the last review in GH when that happens as the reviewed commit goes away.

[gadfort]

It is best to avoid a force push on something that is already in review. I can't see the changes since the last review in GH when that happens as the reviewed commit goes away.

@maliberty sorry about that, will keep that in mind for the future.