Fix inconsistencies between Application path helpers

[jnoordsij]

The Application class has various path-related functions, like configPath and databasePath. A large number of them are also part of the Application contract.

However, I noticed that the publicPath function differs from the others in that

1. it does not accept an argument
2. there is a version in helpers.php that has its very own logic, instead of calling the publicPath helper on the Application class, which actually does accept an argument
3. it is not present in the contract class

I think it would make sense to move all the logic to the Application class and also add it to the contract, but I'm not sure if there are any particular reasons to why it is currently implemented in a way different from the other functions.

[parallels999]

Hi, try to make a PR to 10.x branch

[jnoordsij]

Created #45968 and #45969 to resolve this.