[Bug]: Airports are not the related object / parent of Airport Tiles

[PikkaBird]

Version of OpenTTD

13 rc1

Expected result

Airports and airport tiles derive much of their spec from industries and industry tiles, except in one important respect; whereas an industry is the related object of its tiles, airport tiles have no related object.

This means that although airports have access to station variables including date of construction and cargo information, it is impossible to use those variables to change the appearance of the airport, as the tiles cannot access them. It also makes reusing tiles for multiple rotations a hassle, as they cannot simply access the rotation variable to figure out where they are in the layout.

Please add airports as the related object of airport tiles.

Actual result

It's broken yo.

Steps to reproduce

Try to create an airport newgrf that does anything interesting, and discover you can't.