Add support for WtWSMS' Roman Senate System

[tanner918]

Worth to link, the dev behind the Senate wrote a very nice dev diary about it, if you're interested. It should clear up a bit on how it works: https://forum.paradoxplaza.com/forum/threads/mod-when-the-world-stopped-making-sense-a-migrational-era-mod-for-ck3-476-700-ad.1414709/post-29202186

To adapt the Senate, we should indeed start with a script that dynamically picks some members, rather than predefined ones. As a start, picking the most powerful vassals + maybe your council members should be good enough. It could always be tweaked later.

As for making sure it always make sense:
In the WtWSMS\gui\custom_gui\window_roman_senate.gui file there are some mentions of c_roma and c_byzantion, but these can be replaced by the converter if required.

My idea would be:

• If RE/WRE/ERE holds c_roma, enable the Roman Senate.
• If c_roma is not held by the Romans, but RE/WRE exists, enable and move the Roman Senate to RE/WRE's capital, unless it's c_byzantion.
• If ERE exists and holds c_byzantion, enable the Constantinopolitan Senate.
• If ERE exists but doesn't hold c_byzantion, enable and move the Constantinopolitan Senate to ERE's capital (will require changing the d_senate_east and d_senate_east_adj locs to use the capital's name, or just making it static "Eastern Roman Senate").
  Does this make sense?

IMO the Senate should always be enabled for RE/WRE/ERE on game start. Historically it existed during the Kingdom, during the Republic, and during the Empire

For moving location of the Eastern Senate, could potentially use replaceable code to add in a game_start on_action that saves the ERE's capital at game start as a global variable, then have it change all of the relevant references to c_byzantion to instead use that global variable so that the Eastern Senate could potentially be dynamic based off where the ERE capital is when converting from I:R.

Link to original discussion:
https://discord.com/channels/612683871112396800/692883287336681592/1331421438930059284