Prevent units from blocking refinery dock points and production building exits

Not specific to any particular mod, mainly related to RA and TD where it is a feature and, in TD, a part of balance.

To my feel blocking mechanic the way it is now is quite frustrating, and in case of TD - is actually game-deciding a lot of times, because it is easy to get caught napping with 1-2 fast light vehicles blocking your vehicle production facility as well as refinery so that you have only the option to surrender because you can't produce a response unit and can't get money to produce anything else. Husks left by heavy vehicles only worsen the issue.

This may be a fun mechanic to play with, but it looks just too punishing early game and makes do-or-die situations, taking from gameplay instead of adding to it.

There are several possible scenarios to change it, in case there is a general consensus on it being an issue. For TD this is also a balance question as well, because Airstrip can't be blocked contrary to WF, but has a [significant] delivery delay. Also I assume cases of blocking a production exit and blocking a refinery dock point should be considered separately.

1. Introducing secondary exits to production buildings (obviously doesn't work for refineries). For both RA and TD War Factories there might be two additional exit points, making it possible for a vehicle to pop out into 3 cells instead of 1. This doesn't remove the blocking, but makes it much more invested and thus not really an option for early game at least. This is actually already implemented for barracks exits in TS mod.
2. Explicitly "push" a blocking unit out of the way. This has a lot of possible implications and edge cases, i.e. currently there is no push logic for aircrafts, while it is possible to block an exit with a landed helicopter.
3. Introduce a newly added passable-only cell type at production exit or dock point. Used for TS mod War Factories, same as original.

No source file, test, or entry point is named. Start by comparing the existing TS mod behavior for barracks and War Factory exits with the current RA and TD blocking rules, then assess the three proposed approaches, including refinery dock points and landed helicopters. Done requires a decided design and agreed behavior for production exits and refinery docks.